The trouble I have with the couple proposed solutions for HM moves is that there's a real disparity between how good some HM moves are. Like, yes, Cut and Flash are not especially useful late in the game (though I've found Flash helpful when trying to catch legendaries by bottoming out their accuracy while I spam pokeballs), but Surf is one of the better water moves available to lots of mons.
So, if we add in a fifth moveslot, it gives a real advantage to Surf-learners or even Strength-learners, because they will have access to five viable moves, compared to normal mons or the mons who can only learn Cut, etc. You could force it to not be available in battle, but what's the point of it being a move? Or you could do something convoluted where you could choose to teach it as a regular move OR an HM move, but that's confusing. If HMs get relegated to Key Items, then the moves still have to become TMs to be teachable, or they have to become level-up moves/tutor moves/egg moves. There are also moves that have field effects that are no longer HMs or never were HMs, like Dig, Teleport, Flash, and Rock Smash, so it's not like field moves would disappear if you make the HMs Key Items.
I guess my preferred solution would be to move up the Move Deleter to earlier in the game, in an easily accessed town. Instead of putting him in like the second-to-last town that takes forever to get to, I'd put him in the middle of the game, where Cut is starting to lose its viability, and it would make it easy to shuffle your party around. Alternatively, they could make them overwriteable, but not let you release the last monster you have that could possibly learn it so that you don't get trapped.
Or you could take the route GF seems to be taking and just make them completely unnecessary for completing the game, but I'm an old fart who thinks that's more watering-down of the game's difficulty and BACK IN MY DAY CRIPPLING YOUR PARTY WITH USELESS MOVES WAS JUST HOW THINGS WERE DONE AND WE LIKED IT THAT WAY *waves cane*.
So, if we add in a fifth moveslot, it gives a real advantage to Surf-learners or even Strength-learners, because they will have access to five viable moves, compared to normal mons or the mons who can only learn Cut, etc. You could force it to not be available in battle, but what's the point of it being a move? Or you could do something convoluted where you could choose to teach it as a regular move OR an HM move, but that's confusing. If HMs get relegated to Key Items, then the moves still have to become TMs to be teachable, or they have to become level-up moves/tutor moves/egg moves. There are also moves that have field effects that are no longer HMs or never were HMs, like Dig, Teleport, Flash, and Rock Smash, so it's not like field moves would disappear if you make the HMs Key Items.
I guess my preferred solution would be to move up the Move Deleter to earlier in the game, in an easily accessed town. Instead of putting him in like the second-to-last town that takes forever to get to, I'd put him in the middle of the game, where Cut is starting to lose its viability, and it would make it easy to shuffle your party around. Alternatively, they could make them overwriteable, but not let you release the last monster you have that could possibly learn it so that you don't get trapped.
Or you could take the route GF seems to be taking and just make them completely unnecessary for completing the game, but I'm an old fart who thinks that's more watering-down of the game's difficulty and BACK IN MY DAY CRIPPLING YOUR PARTY WITH USELESS MOVES WAS JUST HOW THINGS WERE DONE AND WE LIKED IT THAT WAY *waves cane*.