RE: Klinklang
I believe that the new Klinklang and the old Klinklang will mix very little. They'll be two seaerate decks, but decks with the new one may tech in a single BW one. Decks based around the BW one won't tech in any of the new ones. The reason for this is that they are support for completely different Pokemon. The point of Klinklang BW is to allow Pokemon of many different types to attack and be healed via Max Potion, allowing it to use the most powerful Pokemon in the format regardless of their type and to hit enemies for weakness. The new Klinklang can only affect Steel types, and there are not very many good Steel types in the format so for the most part they are not worth running in Klinklang BW decks. You've got Cobalion NV, but with Keldeo and Darkrai around his second attack, his main selling point, really just does 80 damage for 3 energy, which isn't particularly good. His first attack can technically let him do lots of damage to an enemy Keldeo, but he's never going to be OHKOing it unless they have 8 energy (7 I can see to OHKO EXes, 8 yeah no) unlike Mewtwo. Registeel used to be good for his first attack, but now Landorus is out and Landorus's first attack is really superior. Registeel EX's second attack is really lackluster, but he'll probably be run in some NeoKlang decks anyway simply because there are no other good steels. Finally, Cobalion EX is coming out, and he seems to be the best Steel type attacker in the game; 100 for 3 ignoring all effects guarantees him a 2HKO on every card in the format, even Eviolited Regigigas EX with Aspertia City Gym out. His first attack is also pretty decent, 30 for 1 isn't spectacular but discarding a special energy can really hurt some decks (most notably BW Klinklang ones, ironically enough).
tl;dr the new and old Klinklangs have no synergy with each other or with the same Pokemon and will be completely separate decks. Time will tell which is more viable, if they're even comparable.