It says that your profile is hidden and, to the best of my knowledge, this prohibits me from sending you a private message.
Yes please, consider me as a strong +1 for a MIDI header. Pins will do perfectly, no need for bulky DIN or over-complicating things, whatever is easier for you.
A few modules that support MIDI also have in/out MIDI as pins on the back (e.g. SDS_Digital Melisma, Bastl 1983 and others) , so being able to connect Hans to them would be ideal with no requirement for direct access to Hans externally. And even if there was a need for that a TRS jack would suffice.
The fact that you have your design power the RPI Zero W from the case, and act as a medium between things is absolutely perfect; that’s why I’m so interested in this, all it lacks is the MIDI pins and the code. If I’m understanding your original aim for Hans correctly, giving access to pins for MIDI in/out “behind the panel” would be in the exact same spirit, right?
Does that mean it’s an either hardware MIDI or BLE situation?
Ideally both, but either is absolutely fine. In a perfect world it would be possible to send MIDI Note information from the Melisma (which is a CV-to-MIDI chord module) and have the Teletype repurpose it, while also (and probably more importantly) being able to sequence the Melisma via CC from the Teletype, without having to plug the two.
The latest beta firmware for the Melisma (not out yet) has more CC options than previously (e.g. Chord List windows are now fully CC controllable) which would allow almost full control via Teletype using i2c > MIDI, with no limitation over cable connections. All I’m missing is the translator!
Another thing that you might find interesting is that Melisma can act as a Select Bus master [1], which would also allow Teletype to control any Select-Bus-capable modules in a system that contains both.
The possibilities are endless! 
That’s just perfect! Being able to edit the MIDI map like that seems ideal. I’d love to beta test this and help as much as I possibly can. I’ll also find a BLE MIDI controller to buy and test on top.
[1] In the video VCMC is sending CC messages directly to Melisma’s MIDI input, which is in turn controlling the Omnimod (screen on the upper left) and the WMD SSM (two modules, one on the top right and one on the bottom left) through the Select Bus.