Well, like someone said, I doubt both Mega Sceptile and Mega Ampharos will be Dragon... One one hand, Sceptile is a starter, and with the exception of Charizard which has 2 Mega evos, PCL is showing to be quite resilient on keeping the starters with their primary types, so M-Sceptile might be Grass instead of Dragon.
On the other hand, Ampharos is the only Electric Mega other than Manectric and while the TCG Grass has both VG Grass and Bug Megas to cover the type, that's not the case for Electric.
There's also the possibility that none of them will be Dragon, as there are so many other Dragon Megas (either released or left to release), they might want to keep it varied.
When I first saw the promo Malamar with theta trait, I went to look it up... It seems an ancient form of the letter is used to represent death... Add that to the color of the trait (purple) and I thought it was chosen due to this set being based around Hoopa... but as it happens, Hoopa EX doesn't have any theta trait. There might be a regular Hoopa card with a theta trait, but still... it's weird for me...
One last thing... Just because there's shiny version of the primals and mega-ray, it doesn't mean shinies are back... For all we know, they can be like the promo shiny Rayquaza-EX. Also, the Mega Metagross and japanese exclusive Mega Gengar promos show a shiny version without any special redesign of the card, they were treated as regular cards...