Most pertinently is the Gravchute. I am part of a Drop Infantry regiment, and I am wondering if I can MIU with my gravchute to get a bonus to operate. It makes sense as the Grav-chutes take delicate precision so I would imagine that the Mechanicus would work one in just in case they had to use it.
What is capable of MIU interfacing, and what is not.
That would be logical. I'd allow it.
Generally, everything can be interfaced with an MIU, if you can get a tech priest to install the necessary modifications. Ham up the "Praise the omnissiah" a bit and help out your engineseer, and it shouldn't be a problem.