Right now the big divide on subclassing is between more casual players who are excited about the idea of getting to roleplay more accurate/enjoyable characters by taking different skill lines, and more endgame oriented players who are seeing both insane power creep AND the nerfing of beloved classes and skills in anticipation of trying to avoid power creep. Right now I see no way of pleasing both - canceling subclassing entirely after it was announced would be a disaster, and if it goes live as is (as of week one PTS), it's a disaster for endgame players. Damage up, Frankenstein monster builds, all while tank specs are in trouble.
My idea to please both is two parts:
1. Take back every single nerf, no matter how OP. Give sorcs back their healing hardened ward, bring dk sustain back up and let them gen ulti during magma shell, revert that warden change from buffing frost damage back to all damage, change templar beam back to the shorter channel, etc. If people want to make insane combos and unkillable tanks, let them. Let them nuke world bosses and harrowstorms and the dreugh king in fungal grotto 1. But also...
2. Disable subclassing in any scored instance (arenas and trials), vet instance (veteran dungeons), and Cyrodiil/IC. Just disable it entirely. Revert all skill lines back to your base class, refund skill points, make people reinvest them. Give them a warning before going in maybe, or save presets for taken skills/passives should you enter a subclassing forbidden zone. This means subclassing is allowed only in overland, public dungeons/delves, quest instances, houses, and normal difficulty instances (I may have missed a few).
For the casual players who do not want to set foot in a veteran dungeon or trial or anywhere with pvp (a pretty high amount of players), this affects them in absolutely no way. You still get your storm calling/winters embrace Maormer storm mage roleplay character to have fun with as you do the new dlc storyline and maybe try to duo the new dungeons on normal with companions. Duelers can still duel with subclassing to test the potential of it on live, and parsers can test overpowered builds on the dummy. But for the places where it matters in a competitive sense: no subclassing.
Think of it this way: if ZOS lets the 170k parses go live and then pulls them back by further nerfing skills, people would riot. "How could they let this go live after we warned them?" World records will get shattered and never broken again (well, not for another 5 years when power creep catches up). We already have another U35 in the making - please don't do further nerfs of skills that will require us to subclass just to crawl back to current numbers.
Versus getting ahead of the issue, realizing the power creep is so SO much worse than they anticipated (I refuse to believe a 50% damage increase is in line with what ZOS expected), and stopping it in scored instances (and Cyro/IC, but my experience is PvE so I cannot speak as much for them) before it's too late. I think players would be less upset getting denied an insane damage increase if it was "just a week one PTS thing" than if ZOS let it go to live and then got nerfed.
DISCLAIMER: I have no clue if this is feasible though. I know using the armory assistant is disabled in scored instances, but I don't know if this kind of idea is even feasible to code this close to release date. What I do know is that right now, subclassing is a mess. Some combos are insanely overpowered with subclassing, while other classes got hit with the nerf hammer in anticipation for subclassing and just made the base class worse. You shouldn't be required to subclass to earn back your power and give up your class identity (daedric summoning...). And if it goes live as is and then gets nerfed, everyone loses. But more casual players really want it for themselves, and at the more casual end of gameplay, it's impact is way smaller. So let it remain in those casual spaces, but rein it in for endgame please!