That being said... Any plans to include mod support?
Yes, we'd like to. While the engine is written in C++, most of the actual gameplay is scripted in
Squirrel, a scripting language with a C-like syntax. In theory, anything from a small mod changing some stats, to adding female characters, to a total conversion could be modded via scripts without us having to do any substantial changes.
However, in practise there is a big difference between us, who know how everything works internally and can adjust the engine to our needs, to script something, and for someone else to do so. The exact amount of modding support (providing an API beyond our own immediate needs, writing documentation, updating our tools to be usable by anyone, etc.) that we'll provide is largely dependent on community demand. Since, again, our resources are quite limited, our priority is to our core game first, but mod support is something we could also add post-release.
My major concern about this game is exp distribution. Given this is "You cannot redo a mission" type game I am curious if I'll need to spread the love or coddle a few elite units (It is actually the only reason I don't play any Fire Emblems... and is the part I dislike most about Wesnoth).
I'm not sure I get what your concern is exactly, but if you could give me more of an explanation I'd do my best to answer your questions.
In general, it is a good idea to have everyone actively participate in battle and gain experience, and not just rely on a few elite units that do all the work. The elite troops + human meatshields tactic might work but a) can easily lead to infectious morale failures which has some or all of your men, including the elite ones at some point, break and flee, and b) leaves you very vulnerable if you just lose one or two of your elite troops. While well-equipped veteran troops will, of course, be harder to take down, they'll never be untouchable to the average enemy or outscale fresh troops by crazy margins.
The exact model of experience distribution isn't something we've finalized yet, but Battle Brothers won't just gain experience for delivering the killing blow (which, imo, leads to very artificial and gamist considerations like keeping enemies alive until the "right" unit can kill it), but for actively participating in a battle.