The only issue is that special secondary stats, while certainly a step in the right direction, is a short sighted fix with our current combat restrictions (i.e. the inability to swap gear mid-combat). That's why I mentioned the example of WoW, and how despite having some alternatives in non-endgame during its earlier years, it is still the same BiS situation that we have right now here.
Player combat is not so intricate to the point that situational gear needs would be a thing. That is, unless fights were created under the basis of needing situational gear.. which, in all honesty, would absolutely backfire. Like mandating your mentioned TP/MP affecting equips because the boss has abilities that drain them. While that would be a new idea for this game (old school to any XI players), the fact they're required is where the backfire begins (and certainly does not end there). I mean, people here got into the biggest fuss over the idea that endgame raid tiers have the audacity to require better gear as you progress through them. At any rate though, as I said, the inability to gearswap is the biggest roadblock to having a prosperous means of horizontal gear progression.
Horizontal gear acquisition in FFXI is both a gift and a curse. It made that equip that you spent months or years (literally) trying to get worth the effort, but it also made endgame into more of an actual job than anything else (old school MMORPGs at their finest). It'd be best to not take that too far, but it's inevitable that it will at some point. I guess what they COULD do, however, is introduce a means to further raise your current gear with augments... sort of like WoWs version, but this will actually raise the ilvl of your current gear. I don't think that'd go over well though, assuming 1 year is too long for one set of armor to be worn lol. That is part of the point isn't it? To have your gear that you worked towards getting be useful for longer.
Let's not forget our current inventory woes though lol. There's a lot they need to adjust before horizontal gearing can be a thing really.