The way the prereleases are going to be done in fates collide is no different from what MTG has been doing with their seeded pack model between Fall 2012 to Summer 2014. The seeded pack in MTG is basically a pack that only contains a certain color or colors, for example, in the Return to Ravnica prerelease, the Rakdos prerelease pack contains a seeded pack with only black and red Rakdos themed cards. In M15, the Red prerelease pack seeded booster contains only red cards. I am guessing the evolution pack contains random evolution lines. In a conventional pre-release with 6 packs, you can't really build a full evolution line because you aren't guaranteed to pull the pokemon to evolve into your stage 2 with 6 booster packs.
I bet that the next changes would be that you have a choice between 2 options that you can choose from, and the promo card is exactly the same card as the theme deck face card, except with alternate artwork. If this were to happen with Breakpoint, you get to choose the Greninja prerelease pack, or the Luxray prerelease pack. You also get to use the promo in your prerelease deck.
Then the next change would be instead of being able to choose one of 2 prerelease packs based on the promo you want, you still get to pick one of 2 packs, except that each one has a randomly inserted promo card drawn from 4 of the rare holos in the set, so 2 different prerelease packs, one of 4 promos per pack, 8 promos in total. The promos don't have alternate art, but is stamped. The change is instead of getting one promo, it goes back to the fates collide version of randomly giving you one of 4 promos, with the difference that you have 2 prerelease packs to choose from, each one with a specific set of 4 promos, in which one of 4 is drawn randomly. At this moment, the theme decks would have alternate art for their face cards, but still have a non-holo second copy of the card with regular artwork.
The last change is instead of having 2 different prerelease pack choices to pick from, you only get one. The pack contains 6 boosters, no evolution or special packs. Just 6 plain old boosters. Instead of having a one specific promo card or one of 4 promos, the promo is any random rare-holo from the set. The promos are stamped.
Just watch how all this is going to happen haha.
For the last changes, even if it isn't prerelease pack, Yugioh does have a Super Edition where the promo is any random super rare from the set.