They still could lock things that are set in stone, and let us adjust the rest. O_o
That does sound good, and there aren't that many things that are set in stone, now that I think about it.
Shadowheart's Diety is absolutely locked in, but she doesn't strictly need to be trickster domain. Wyll has to have a fiend patron, but we could pick his cantrips and his spells. Same goes for all spellcasters, really. Picking Lae'zel's fighting style would bring some welcome variety. Astarion has nothing to change aside from his proficiencies.
Is changing proficiencies going too far? After 200 hours of early access I'm voting no, but it could be because I crave variety after playing the same encounters in the same way over and over.
For it to make sense, storywise, it could be part of the tadpole's effects. No need for the awkward "I can fight like this, or like this, or like this" dialogue from DoS2.