I feel like we should make things easy and I don't understand why we are trying to jump through hoops to over complicate things.
Use the KISS technique and go with 3 formats: Rebellion (Current Block), Modern (2 blocks), Wild (all cards).
I don't see a need for "Classic" at all. Alpha holders were already rewarded for YEARS with all the benefits that came with those exclusive tournaments (and don't get me started on the SPS airdrop!), and now those cards can all be used on lands, or in Wild! To say that would Alpha cards no longer have a purpose is completely disingenuous since the GOOD cards will still be played in wild! I don't know of anyone who would say that owning Master of Waves, Lord of Darkness, or Spirit of the Forest doesn't give them a competitive advantage over those who don't have them, and therein lies their continued value. I feel like I've been saying this forever: Good cards are good, bad cards are bad. You don't want to create formats just to artificially add value to cards like "Animate Corpse" which are just outclassed these days.
The whole premise of "classic" existing to keep older sets relevant (or something?) is flawed, as that the cards are still playable in wild (see above). In less than a year from now when the new set comes out, Chaos Legion will rotate into it allowing the masses to play in this "classic" format anyways which certainly doesn't make it "classic" anymore.
It's not flawed because power creep is evident in Rebellion. It could be worse, but it's definitely there, and realistically there will be more of it in any upcoming mini set + future main sets. I think early investors deserve to have the chance to remain competitive in at least one format if they put thousands into the game, without being expected to spend more every year or two. They might have some strong Alpha or Untamed cards but not have spent anything on Rebellion or CL and therefore even with LOD or SOTF they might lack enough cards to keep up with Rebellion's meta changing abilities. I say this by the way, as someone who only entered the game at CL so most of my deck is CL, but who has picked up quite a lot of Beta and Untamed cards yet only has a single Alpha card.