There is currently no way to test if there is anything inside of a pressure chamber (calling it PC here on out to save my terrible typing) automatically, let alone what is inside of it. Not even basic comparator logic can do so. I would appreciate a way to test the following:

1. If PC has anything in it at all.
2. If the PC has a valid recipe but not enough air.

These could be done with a comparator and differing redstone levels, fancy redstone could then just turn the interface on once given the go ahead until the interior is empty. Maybe even add a redstone interface block for such things.

I would also like to see its contents exposed through the OC and CC compat so they can control the interfaces either through redstone or even changing interface modes.

Yeah, such comparator support is a good idea. Probably have a level of 1 if there are any items in the chamber, and 2 if there's a valid recipe but insufficient air.

Note that there's now a redstone module for pressure tubes which allows the tube to transmit redstone (and with an Advanced PCB, carry out various more complex logic operations).