Settings that 5e won't officially get:
Mystara-Known World-Hollow World; Al-Qadim; Nentir Vale; Birthright; Dragonlance. For M-KW-HW and DL there's the question of whether they own all the associated IP; Al-Qadim might raise cultural-appropriation questions these days; and Birthright almost needs its own separate rule-set. As for Nentir Vale, they could do this one but I'm still betting they won't.
I somehow think they will eventually release 5e versions of Spelljammer, Planescape, Dark Sun, etc.
Races and Classes:
I'm tempted to say for both of these that if it isn't already out there, don't plan on seeing it in its original form. Some old classes might at some point be made sort-of possible by the right combination of subclasses and feats maybe, but that's it. For sure we'll never see race-as-class a la 0e.
Items that 5e won't officially get, at least in anything close to their original form:
Sword of Life Stealing (it drained levels on a hit; so to bring this in means bringing back level drain)
various Librams, Tomes, Books etc. that bestowed levels to or drained levels from the reader (ditto)