Would love this since it would take me back to using Amiga trackers - would also help make putting in notes much quicker.
Has there been any plans to implement an expander for this? I'd buy one in an instant.

Or perhaps support for a ps/2 one instead, or allow customisable commands that rely on MIDI messages?
Message recover:
USB keyboard should be no problem, but is not on top of my 2do list.
A general USB interface add-on for keyboard input and Midi I/O or perhaps even as a general purpose, multiport USB interface for the Nerdseq to talk to a computer would be great (for project management, sample management, and the like, as well as firmware updates or whatever else as an alternative to removing the sd-card). I imagine being able to use USB storage media through such a device might prove useful, as well. Additionally, USB to video adapters also exist. Obviously I don't know how doable any of this is over the Nerdseq's expansion ports, but I would certainly be more inclined to use a USB add-on if it had a multitude of functions.
NerdSEQ is not a high end computer where i can use a full fledged USB stack. I something will come some day, then it would be some external device with limites capabilities. USB video wouldn't work anyway, but probably USB-Midi and Keyboard support. But those would also be 2 different adapters. And all not on top of my 2do list.