When 5th first came out and WotC started publishing modules with rules on how you could run this game using 3rd or 4th ed rules I thought that there would be hope for games that used different rulesets. But with 5th being the most popular that hope died there is approximately zero chance that wizards will want to allow a game based on a less popular set of rules.
And even if that was incorrect I doubt they would choose 3.5. Most 3.5 fans prefer Pathfinder and have even started calling PF 3.75, the edition that WotC should have created.
OP, I see you haven't played Temple of Elemental Evil -- you need to. All of the critiques are valid -- no story to speak of, bad writing, annoying bugs but as a 3.5 rule simulator it's unparalleled. (make sure to grab the fan made looting bug fix)
But I'm a 2nd edition partisan and I think 5th is the second best. In 5th it's easier to lose feats -- in 3.5 if you chose the wrong feat you are locked into into it. In this the DOS2 ruleset was better -- don't like your build? Go to the respec mirror rebuild yourself.
2nd didn't have this problem. Not happy carrying around the Shield of the Fallen Lord and helmet of telepathy? Take them off and put something else on. Do a quest and get shield you really like. No need to locked into a decision you made 5 levels ago.
let me tell u how out dated 2nd edition is.
You cannot multiclass if you are a human not at all.
No, humans can dual class which is much better. Want to rule Throne of Bhaal? Build a cleric to level 17, dual class to mage. That build can take on the gods themselves. Want to tell a story about the rogue who went legit? Build a thief to level five and dual class.