IMO that would bad in term of performance, for a minimal gameplay improvement..

I don't see any reasons why it would be faster, since jettison function dissociate the door from the helicopter; opening door could hinder the crew, or be difficult in case of hull distortion.
Anyway, these are useless details.. I agree with u about the underwater thing.

Very few ? Read my PDF's pages 10 and 11. I'm sure Ka-60 has this feature too.
As said before i'm not requesting a parachute eject feature which is not realistic on a large number of helos (except Ka-50/52), but a eject options for low alt/speed emergency situations.