I don't think ability to change base class for a companion will be of utmost importance
Come on now you do it for purpose. :-/
Rag wants to play the with the companions to come, and don't wanna wait anymore.
Well ... basicaly.
I dont mind waiting, i just thought it would be fine compromise ... even tho i have to admit it pisses me off that once you want to go through Evil route you practicaly loose up to two companions ... yet if you are good, everyone is complaining but stays with you loayal as a dogs. -_-
He doesn't care if their dialogues would clash with some placeholder class than what they are supposed to be in the end game
What do you mean exactly? O_o
There is nothing holding character to have Paladin tag while being Fighter ... both systematicly (as Chubblot showed us in his videos) and lorevise, since there is multiclass.

The only thing that will be missing would be combat abilities ...
They totally can get all [Paladin], [Barbarian] and [Bard] dialogue options they should have ... they probably will not have advantages where their classes should, but there is allways cost if you wish to play with placeholder. :-/