So guys, I've got a MIDI controller that I think would be useful if it could be brought into some live situations. So I'm a bit into the idea of getting an Arduino / Raspberry Pi and building a Linux MIDI module that'd run Xpand!2. In my mind, it'd be much cheaper and actually possibly better in some cases than investing in a "legit" module.
Has anyone explored this? Any tutorials or information about a project like this out there?

I guess that depends on what your time is worth. Roland is selling their new D-50 clone, the D-05 for $350. That's hard to beat.

I believe it's very common, most will be using a laptop or an iPad but a mirco box PC would be OK. Only drawback is you will also need to drag a monitor around too. I use a little Netbook for live playback. I haven't run live soft synths but no reason it wouldn't work with a good audio interface connected. 
You can use Sonar as the VST host but there is also software designed just for this  ( Reason? ) 

Every time I see "Arduino" I think of Evan Kale. He has done a lot of off-the-wall projects (many at user requests) and tends to use Arduino in a lot of them (and posts the coding for them). It may be worth touching base with him. His email is listed in his YouTube channel IIRC, so will not post it here out of respect for privacy.

rsinger
I guess that depends on what your time is worth. Roland is selling their new D-50 clone, the D-05 for $350. That's hard to beat.

In fact I found a mid-90's Roland module for VERY cheap. I really only need to have something to bang out ideas on with my MIDI controller every once in a while like I could when my full-size keyboard was hooked up. I think this unit will do the trick! :))

A mid 90's so is it a sound canvas? those were pretty cool in the day and I used one for my "band for a few years..  a mid 90's sound module in a way should be free :) . But I now see what you were wanting to do and that's a perfect solution. I still use my Korg o5W just like that. It is also about the same vintage.  

Cactus Music
A mid 90's so is it a sound canvas? those were pretty cool in the day and I used one for my "band for a few years..  a mid 90's sound module in a way should be free :) . But I now see what you were wanting to do and that's a perfect solution. I still use my Korg o5W just like that. It is also about the same vintage.  

Yeah, it's a Sound Canvas - I was surprised from the demos at how nice it actually sounds. A LOT better than some of the GM stuff built-on on soundcards, and it seems to be about on-par or a little better than TTS1, albeit lacking a number sounds and having a few really wonky sounds in comparison.
 
However I did get the idea of buying a Windows 10 tablet with USB ports, loading a VST host on there and using that. It's extra dangerous relying on a single 1/8" headphone jack-output and a 10' screen, but the fact that a host could run on there could make it an actual option for a live setup. It's been done with iPads... I *just might* give it a shot with my iPad and USB adapter to see how it could function.

UPDATE::
BUST!!! Anyone know if Roland is still repairing these things?? At this rate, I don't feel like it'd be wise for me to sink any more cash into it. I got this one on the relatively-cheap knowing it hadn't been tested - guess I got what I deserved this time around, and it'll be a good lesson for next time

Whoops! Doubt if they can be repaired, Most often someone uses the wrong power supply and fries them. 
 
The tablet idea is good. I use a little net book with a 10" screen and often have used the 1/8" jack powering a
 PA systems without issue. I don't get any hum and the fidelity seems the same as when I use an audio interface. So for basic gigs and stuff I still use the mini jack. I just bought a Radial DI that has 3 types of inputs for use with portable devices. 
https://www.sweetwater.com/store/detail/TrimTwo