Ive modified one of my Dreamcasts to have a DreamPSU, GDEmu, Noctua fan and upgraded controller board, as well as internalizing a BlueRetro solution thanks to the awesome work by DarthCloud. Only caveat right now with BlueRetro is that it does not currently support/provide a VMU solution. The dev did mention that is something he'd like to look into but it's basically on the backburner at the moment.
After replacing the PSU and the GD assembly, there is quite a bit of room in console. The ESP32 board for BlueRetro fits nicely in there, and it looks like there's probably plenty of room for a standard sized VMU in there as well.
My thought is there must be a way to basically hardwire a VMU onto the controller board, or maybe straight to the motherboard. But I'm not certain if that's possible. Searching the net for 'hardwired vmu' brings up one reddit thread that basically asks the same thing I do, and hasn't been updated in about a year. Has anyone thought about doing this, (or actually done it)?