But I've always had a lingering feeling that it could do a lot more..
For what little it's worth, I suspect it's always going to be a bit niche. For me, I like the idea of a sort of halfway house between building documents with boilerplate sections chosen as required -- my first experiences of wordprocessors back in the <cough> early 1980s included interacting with the bits of them that allowed such things, even if I didn't use them very often -- and full-on mailmerge. But I'm not an ordinary user, and I quite often find myself diving headlong into things I don't know much about in order to solve a specific problem. TFLM was what seemed to be the best fit to a problem I was trying to solve at the time, and even with its limitations was very helpful. I haven't needed to do anything else like that since...
The Form Letter Machine is one of my apps that I regularly think about rewriting from scratch to be much more powerful and flexible. In fact I have rewritten it once as a fully working web app (tfdocs.com) that was pretty sophisticated, but that was abandoned due to lack of interest/funding/etc.
I did go look at the time, I think, but couldn't see a good reason for moving the sort of things I could envisage wanting to do off my local PC.
More flexible support for custom scripting and variables would be a key focus of any rewrite, and probably making it cross platform (mobile?), along with multiple output formats (pdf).
I think if you could do variables and (basic) formatting -- text enhancements, tabs -- and output in .doc format, or plaintext too, I guess, most people who'd have a need for something like TFLM would be able to take it on from there, wouldn't they? And the cross-platform thing -- you could be right but it doesn't strike me as an obvious need.
Anyway, the difficult dilemma for me is deciding whether its worth the effort to write a new version, and how much time I could spend on the project...
I guess if it's a "from the ground up" sort of a problem, it's probably never going to justify the extra work. It IS pretty good as it is, for the six people in the world who use it
Thanks for thinking about it, anyway!