So I've been thinking about this more, and I'd like to throw out a question to the more experienced, veteran pokemon players:
Has pokemon ever had a time in its past where it's only carried 3 or 4 expansions in its Standard format?
If yes, then I think we should be prepared for a rotation through Evolutions. If not, then we'll probably still have everything Breakthrough on.
Right now, my money's on Breakthrough on. I really doubt that Pokemon's going to rotate out 8 or 9 expansions. It's just going to <bleep> too many people off.
There was a format with Sabledonk which forced them to remove all of the remaining D/P/Pt sets (both pre and post SP) and go right to HGSS-On. The rotation was also done 3 to 4 months ahead of normal rotation. This was due because of Sableye and new rules/mechanics of the block. This is why I believe rotation will be Evolutions-On.
Going to be real. I think essentially rotating everything released prior to October 2016 seems like a terrible idea. There was a lot of money invested in those cards and to only get one season of play from them is ridiculous in my opinion. Honestly, I think losing VS Seeker + Trainer's mail alone does a metric ton to slow down the format. Add Shaymin to that list and I think the format will naturally be slow even rotating 4 sets.
I would stop looking at things as "X spent money" so we can't do this. We all spend money on the game, some more so than others. I personally spend thousands on singles in the past year or so and they will rotate out. This is just the simple nature of card games like Pokemon. We also have a expanded format where all of those cards can be used. Yeah, it will suck but if its for the betterment of the game, then so be it.