After playing a tri-form, bi-form and human PB in the level 40 range I can not find any good reason to keep the forms.
If they worked in conjunction with my human powers the I could see a use for them.
Warshades work fine as triform admittedly, because thay carry pets and buffs over from human to the forms.
Why would my suggestion make forms less unique?
It would just make the AT a bit more appealing to the average player and make slotting a keld less of a ball ache.