We can already do that. We’ve been able to send catch up gear to alts for years.
It’s a talent tree for a companion. Not what your individual characters specifically do.
We already have account wide achievements. It’s never stopped me from playing other characters nor does it affect my other characters.
This has also been a thing for years. We’ve got toys that unlock flightpaths and finishing MSQ would unlock main hub flightpaths.
This didn’t affect me playing other characters.
And you will not get tier from that nor class specific unlocked. So it still doesn’t affect me playing multiple characters.
No. Ion has been adamantly against account wide stuff and only recently gave in a bit.
Questing on one character doesn’t change questing on another character.