>>47175655I'd go the complete opposite route and refine what we already have.
>Gen 61. Make areas that were clearly cut for time accessible, i.e. the wasteland power plants.
2. Give Pokemon that don't have Megas an alternative power-up that boosts their base stats by 10 each.
3. Make a proper Pokemon X2/Y2 that fleshes out the region with a few new areas and deals with Malva reviving Team Flare using her celebrity. Relocate the Zygarde cell hunt to these games, make Magearna a mythical available here.
4. ORAS gains all Emerald improvements and a proper Battle Frontier.
>Gen 71. Megas are now a permanent part of the games' battle mechanics and are introduced to the player relatively early on in the story. Each new game from now on introduces at least 7-8 new Mega evolutions, focusing on the previous generation's mons.
2. Make dedicated Physical, Special, and Status Z-moves for each of the 18 types. Also, maximum length of Z-move animations in strictly 5 seconds.
3. Sun & Moon need serious refinement. Restore cut areas like the tidal pools, golf course, power plant, and Victory Road. Give Mina a proper trial and create an eighth trial so that Island Trials feel like a full analogue to gyms.
4. Mega evolution of Nihilego into something resembling the Mother Beast. And while we're at it, actually fighting the Mother Beast.
5. USUM's remains an alternative retelling of SM. The big new addition is the ability to sail between islands, encountering smaller islands, diving spots, and other landmarks along the way.
6. LGPE is actually fine in its role of introducing Go Players to simplified game mechanics, but allow cross-gen evolutions of Pokemon like Golbat or Scyther to take place.