Ah the problems with this one!
Okay so the really big thing here is THERE IS NO DRAGONBORN DURING ESO/THE INTERREGNUM and IT TAKES PEOPLE YEARS TO LEARN THE DRAGON LANGUAGE AND TO BE ABLE TO SHOUT, THE PLAYER CHARACTER IS NO EXCEPTION AS THEY ARE NOT DRAGONBORN.
Companions as a guild with an ability line seems interesting but probably wouldn't be much different than the Fighter's Guild.
Alduin is still cast adrift in time and cannot be anywhere in the second era...
Also really? Honestly if you want all that, just go back to Skyrim.