I’m going to present a more radical idea altogether: What if we didn’t have TMs at all?
Now, I’m not saying this is necessarily a good idea, but the question with this discussion has been how to handle TMs. Yet in my opinion, TMs are simply a somewhat fundamentally flawed mechanic and a bit of a relic from the early days of the game. Not only does the very idea of TMs not make much sense lorewise (how do they work again?), but they have some core design problems from the get-go, regardless of the type: limited TMs offer strategic value, but heavily punish you for the ‘wrong’ decision and make entering competitive play near impossible, while infinite TMs have potential to trivialize the game (see: Scald in SM) and have no stakes attached to using them.
Now immediately, two problems are presented: TMs not only offer movepool diversity, but also provide incentive for exploration. These two issues must be addressed if TMs are to ever be theoretically abandoned. Here’s what my idea is:
TMs are replaced entirely by tutors, which would be greatly expanded upon. Tutors, like in ORAS and USUM, now accept BP as their currency of choice, but BP would be greatly expanded upon; you now obtain a given quantity from gyms. Let’s say for the 1st gym you earn 100 BP, and the town has two tutors. The first teaches Work Up or Calm Mind, each for 50 BP; you can learn both moves with your given BP. The second has a more powerful move: Ice Beam. However, Ice beam costs 100 BP, meaning you give up the use of Work Up or Clam Mind. This idea lends itself to more strategy and decision making without the permanance of pre-Gen V TMs. In addition, several battle facilties could be added throughout the game as additional, but ultimately minor sources of BP. And for beating the Champion, perhaps you could basically obtain the league’s credit card and be given a potentially infinite amount of BP, meaning that you have a permanent source of moves.
As for exploration, this could be remedied by simply expanding upon Mega Stone and Z-Crystal hunting. Every Mega Stone and Z-Crystal could now be available in areas in the wild, with none as handouts. This makes the process of obtaining all of the Mega Stones and Z-Crystals more rewarding to find, and allows the games to detach Mega Stones and Z-Crystals from the plots of the games as they do each generation.