i also think it'd be nice if we could have the same system used to form adventuring parties add retainers into the mix.
it would give people more incentive to pay that cheap price for additional retainers. so things like picking retainers and squad members to party up with you out in the world or in a dungeon / trial / raid could also help with duty queues that sometimes take quite a while.
heck sometimes it hard to just find enough people to party with in heaven on high much less some of the less some of the less queued for trials.

i do think that people should be required to make it through certain content/duties with their own companion party before they're allowed to mingle a companion/squad party with other players (should the players choose to allow it for quicker queue times similar to the undersized party option)
to be perfectly honest there are things i wouldn't want to run with AI tanks/heals and things i certainly wouldn't mind.

it'd obviously cost grand company seals and ventures but return experience for the members of the companion party. even if it had a two hour at a time limit or something.

honestly though sometimes even just having a decently set up AI tank or heals would shorten queue times for everybody quite a lot. there's an overabundance of dps as is usually the case so i think it'd be worthwhile especially considering it could also open up some interesting options for new mini games.