No the eJ Buses will NOT come with airstairs. The stairs on the Bus are very steep and open-tread, so not ideal (or safe) for high volume operations. They are also expensive and add weight.
There is no reason for the A319 turnround to be any slower than the 737 (and can be quicker if the ground support is right).
Sure, you may lose a minute positioning forward steps compared with deploying airstairs, but then boarding up/down mobile steps is quicker than steep narrow airstairs, so you get that time back. Also the aisle is wider and the overhead bins larger = quicker boarding.
As for the baggage, the hold is far easier to work in (and the cargo door far more central to the rear hold than on the 320/1) so the whole baggage process will be easier.
So why should a 319 t/rnd be slower than a 737?