This idea is related to the I/O Window. At the moment in pro tools there are a number of issues with Aggregate devices. Often when using multiple audio interfaces in OS X 10.11 the I/O doesn't match with the devices in the I/O window. This can make determining which input is which incredibly difficult.
My suggested solution is two fold.
One - make it so that aggregate device I/O and the I/O correlate with input names - so all analogue and digital inputs actually line up properly.
Two - Add input monitoring in the form of a meter strip in the I/O window, so you can quickly determine by playing an instrument or tapping a mic, which input is each, so you can label them up easier. Also, have an input monitoring button within the I/O window so you can listen to the audio as well as see it from this window. This would make setting up I/O much quicker and simpler for projects as when using multiple audio interfaces it can be very easy to get lost, and very time consuming to work out what audio is coming from where.