Can this be done without too much pain and suffering?

It may seem a little silly, but updating nullai upon engine version releases is rather tedious to some extent. Other than being it's regular old useful self, does it serve any other purpose than for gamedevs to use in testing?

yes
http://springrts.com/wiki/AI:Development:Lang:Lua
but you can only add it via lobby

The primary purpose behind NullAI and its like is to demonstrate the most primitive AI. Its intention is to act as a starting point for an AI that isn't null. That it's good for testing is merely a secondary use.