Having just watched The Swarm last night, that episode at least hints that the program is massive and hugely complex and not for long term use. B'elanna did some jiggery pokery to keep it stable that failed after two years. I'd imagine if you start adding extra programs to that
Thinking about it, the episode makes it quite clear that the fix for the EMH they do is temporary at best, and likely to fail further down the line.
My question is, why doesn't someone develop one for Engineering, an EEH if you like (which you probably don't)? Imagine all the problem in there that go wrong that's too dangerous when everyone has to abandon the place. Having someone who can stay there and keep working would be a hell of boon, way more than an extra pair of hands the EMH was designed to be.