lots of good ideas here, but most of it would require drastic changes and i therefore doubt they will even consider it. The real problem is that someone at CG absolutely loves the hero deck. players have been saying remove the hero deck ever since dungeon defenders eternity and it falls on deaf ears. it creates massive problems and eliminates build diversity even w/o considering rift mode.
the simplest solution?
1) xp toggles. players can gain xp on X number of heros which can just be toggled on/off. it's still limited but has nothing to do with a hero deck. done. simple
2) completely remove the hero deck in its current form. the "list" of heros we can choose from (our entire hero list) becomes the deck. they will soon allow us to re-sort that list, perfect for this solution. now in keybinds we can assign ANY keys we want for the hot swaps. F1-F12 by default(still fully customizable) would make sense for the first 12 slots with any further slots being blank by default. then we can assign literally anything we want to swap between any heros we want. if i wanna swap to my 30th hero slot with the V on my keyboard? sure done.
The biggest problem with things as is, is that build diversity doesnt exist. even w/o rift mode. once you're end game you focus on speed builds. so for example on glitterhelm that means we have 4 major points of defense. if we want more than 4 heros used, we must run to a spot, build, swap the deck around for more diversity, finish building, then run to the next spot and reswap the deck all around again. all that deck swapping adds a TON of build time. the end result is no diversity at all. players refuse to waste time swapping the deck around roughly 8 times during the build phase to get what they really want. instead we limit ourselves to the 4 in the deck and only build what they offer.
the end result? when i run glitterhelm i use 2 monks, 1 EV, and 1 apprentice. i never swap them for any reason as that wastes too much time farting around with the hero deck. so all those extra very specific characters ive made? they're all wasted. i think ive got around 30 heros at this point, all of which have very specific purposes. unfortunately im pidgeon-holed into using none of them because of terrible game design. ideally when running glitterhelm if i actually had my choices, my build would include 3 monks, 2 huntress, 1 ev, 1 squire, and 2 apprentice. that's 9 heros i would use and im stuck with my crappy 4 heros option. terrible terrible design.
but again, this has been beat to death by people dating back as far as dungeon defenders eternity. someone at trendy/cg thinks the deck is great and we will never be rid of it. it stamps out build diversity, makes gaining XP a nuisance, and encourages people to narrowly focus on 4 characters even if they have 30 like me. it has absolutely no upside. some of the ideas of the OP would give it upsides and are good ideas. however i dont see them ever implementing such complicated systems as they would require a lot of work.
my solution is simple, would require very very little work, and fix all of the real problems with the deck.