I disliked this feature in DOS 2, since it stripped down all the companions of of most of their identity.
I feel it would be an even poorer fit for the D&D ruleset and setting.
Not everything that is convenience for the player on the immediate distance makes a game better.
And let's be honest... The feature was in DOS 2 to compensate for the extremely low number of companions available, the mere suggestion it will be in BG3 hints at a similar problem.
Besides Helia and Karlach, I don't see any other character that is in the works to be a companion

I hope they take your suggestion to heart