Sorry for the double post, but thought as long as we have this conversation going this should be posted. As far as I know this is a full list of stuff that can, but does not, have an alternate typing in tcg. If I missed something feel free to mention it. This lists ignores the technically unrevealed Hoopa and Volcanion.
Venusaur line- purple psychic (poison)
Charizard/M Charizard Y- white colorless (flying)
Charizard X- fire red
Butterfree- white colorless (flying)
Beedrill line- purple psychic (poison)
M. Beedrill (mega not even out yet, will likely be grass)
Crobat line- white colorless (flying)
Vileplume- purple psychic (poison, Oddish and Gloom were made but are out of rotation)
Venomoth line-purple psychic (poison)
Victreebel- purple psychic (poison)
M. Pinsir- white colorless (flying, of course we don't have this mega at all yet)
Gyarados- white colorless (flying)
M. Gyarados-(of course we don't have this mega at all yet, water is more likely that dark imo.)
M. Aerodactyl- (no way to know which form this will come in actually. We got a colorless Aerodactyl ex but never a fighting one)
Articuno, Zapdos, Moltres- white colorless (flying)
M. Mewtwo X- (likely will be fighting type, which means we'd need psychic)
Ledian line- white colorless (flying)
Ariados line- purple psychic (poison)
Cleffa and Igglybuff- pink fairy (could happen but babies have been non existent since HGSS)
Xatu line- white colorless (flying)
M. Ampharos- electric
Jumpluff line- white colorless (flying)
Steelix- brown fighting (rock)
M. Steelix- (mega not out at all yet, I think will be steel though)
Qwilfish- purple psychic (poison)
M. Heracross- brown fighting
Sneasel- blue water (ice, oddly Weavile did get one of these, it is out of rotation though)
Corsola- brown fighting (rock)
Mantine- white colorless (flying, includes Mantyke but we've only had one of these in DP, no babies since HGSS anyway)
Skarmory- white colorless (flying in Roaring Skies)
M. Houndoom- (mega not even out at all yet, I suspect will be dark though)
Tyranitar- brown fighting (rock, only one of these was in TR called Dark Tyranitar, long out of rotation also personally would prefer a general over a dark classification)
M. Tyranitar brown fighting (rock, dark is in Ancient Origins)
M. Sceptile (mega not even out at all yet, it's anyones guess on whether it will be grass or dragon)
M. Blaziken (mega not even out at all yet, it's anyones guess on whether it will be fire or fighting. At least fire type confirmed.)
M. Swampert (mega not even out at all yet, it's anyones guess on whether it will be water or fighting. At least water type confirmed.)
Beautifly- white colorless (flying)
Gardevoir line- pink fairy (In Ancient Origins)
Masquerain- white colorless (flying)
Nincada- brown fighting (ground)
Ninjask- white colorless (flying)
M. Sableye (mega not even out yet, it's anyones guess on whether it will be psychic or dark)
Azurill- pink fairy (unknown if this will happen, no babies since HGSS)
Mawile- pink fairy (will likely happen, mentioned for completeness)
M. Mawile (mega not even out yet, it's anyones guess on whether it will be steel or fairy)
Aggron line- brown fighting (rock, there is a line in Aqua/Magma as steffenka reminded me, thanks for that
but I would like a general line instead of a trainer line not to mention that this Aggron was fighting/dark which is as unofficial a typing as Delta Species pokemon. There is another Magma Aggron line expected in Double Crisis.)
M. Medicham- (mega not even out yet, it's anyones guess on whether it will be psychic or fighting)
Camerupt line- brown fighting (ground)
M. Altaria- (mega not even out yet, it's anyones guess on whether it will be fairy or dragon)
Cradily line- brown fighting (rock)
Armaldo line- green grass (bug)
Tropius- white colorless (flying)
M. Latias (not out yet, dragon seems likely)
M Latios- purple psychic
Primal Groudon- red fire
M. Rayquaza- (both types surprisingly in Roaring Skies.)
Bastiodon line- brown fighting (rock)
Wormadon Rock/Steel- green grass (bug)
Mothim- white colorless (flying)
Vespequin line- white colorless (flying)
Gastrodon West- blue water
Gastrodon East- brown fighting (ground)
Drifblim line- white colorless (flying)
M. Lopunny (mega not even out yet, it's previous forms are colorless but this one is fighting as well, so who knows)
Skuntank line- purple psychic (poison, there was a Skuntank only as steffenka reminded me, and thanks again for that
though I would prefer a general type as well as the fact that there is no Stunky as this was an SP pokemon.)
Mime Jr- pink fairy (no baby Pokemon since HGSS, so who knows if this will happen)
Garchomp line- brown fighting (ground)
M. Garchomp (mega not even out yet, I suspect will most likely be dragon)
M. Lucario- silver steel
Yanmega line- white colorless (flying)
Gliscor line- white colorless (flying)
Frosslass- purple psychic (ghost)
Rotom- purple psychic (ghost)
Heat Rotom- red fire
Wash Rotom- blue water
Frost Rotom- blue water (ice)
Fan Rotom- white colorless (flying)
Mow Rotom- green grass
Giratina altered form- gold dragon
Shaymin Sky form/Skymin
- white colorless (flying will be an EX in Roaring Skies, no regular one though)
Arceus- gold dragon and pink fairy (personally I think this will happen eventually)
Pignite/Emboar- brown fighting
Swoobat line- white colorless (flying)
M. Audino (mega not out yet, previously colorless but as a mega can be fairy, not sure what it will be)
Papitoad/Seismitoad- brown fighting (ground)
Scolipede line- grass green (bug)
Whimsicott line- pink fairy (In Ancient Origins)
Darmanitan Zen mode- red fire
Scrafty line- brown fighting
Siglilype- white colorless (flying)
Carracosta line- brown fighting (rock)
Archeops line- white colorless (flying)
Swanna line- white colorless (flying)
Sawsbuck line- white colorless (normal, also missing Fall and Winter season forms)
Emolga- white colorless (flying)
Escavalier- green grass (bug)
Amoongus line- purple psychic (poison)
Jellicent line- purple psychic (ghost)
Galvantula line- grass green (bug)
Ferrothorn line- grass green
Mandibuzz line- white colorless (flying)
Volcarona line- green grass (bug)
Cobalion- brown fighting
Virizion- brown fighting
Thundurus, both forms- white colorless (flying)
Black Kyurem- blue water (ice)
White Kyurem- blue water (ice)
Keldeo, both forms- brown fighting
Genesect- silver steel
Chestnaught- brown fighting
Delphox- purple psychic
Flechinder/Talonflame- white colorless (flying)
Vivillon- white colorless (flying, also missing multiple patterns that we'll likely never get)
Pyroar line- white colorless (normal)
Aegislash line- purple psychic (ghost, including blade and shield form)
Malamar line- purple psychic
Barbacle line- blue water
Skrelp- blue water
Dragalge- purple psychic (poison)
Heliolisk line- white colorless (normal)
Tyrantrum line- gold dragon (I think this will happen in time, EX promo to be released)
Aurorous line- brown fighting (rock)
Hawlucha- white colorless (flying)
Carbink- brown fighting (rock)
Trevnant line- green grass (granted we have Trevnant EX in Primal Clash, but no Phantump)
Pumpkaboo line- green grass
Noibat- gold dragon
Noivern- white colorless (flying)
Yveltal- white colorless (flying)
Diancie/M. Diancie- brown fighting (rock)
Zygarde (not in at all, mentioned because this annoys me and because it will only likley be dragon despite also being ground)