I'm hoping that they leave some of the more Legendary characters out of TES: O, so we can see/fight against them in the single player TES series. I'd be pissed if they finally showed Lamae Beolfag/Bal (i thought for sure that Dawnguard would show her), and she just ended up being some boss in a dungeon we end up killing. It'd take away from her epicness if we could just kill her over and over and over again in an instanced dungeon.

Btw, wtf is up with them showing the King of Worms (Mannimarco) as a High Elf? In TES II: Daggerfall and the lore books, Mannimarco is a Lich, while in TES IV: Oblivion and TES: Online he's a Altmer.

They arent like that... ESO's bosses are more advanced normal monsters, at least some of them, I'd almost bet all of them, they didnt design this to be boss/raid game. Keep in mind though, theres group/raid content and bosses but bosses arent so damn unique and epic.

From what I can gather all the Lich from Obilivion TES IV were Ayleid and not Altmer. http://elderscrolls.wikia.com/wiki/Ayleid Which is why we probably never see the Liches in any of the other games, because they are all in Cyrodiil. Just another misshap with the lore from ZOS possibly ?

With the game being set a few thousand years previous to the other single player games it gives them a lot of leeway to what they can put in and do. Vampires are considered to be difficult to kill look at Morthal in Skyrim and the vampire lair you are sent to in that hold. The vampire lord was apprantlly killed before and has risen again. So it is possible for Lamae Beolfag to be in TESO and in latter single player games.

As for meeting Daedra thats going to happen no matter what TES game you play they do love to toy with the mortal races.

You can realistically just pretend anything that happens in TESO never happened in your singleplayer games at all.