OK, thanks. That's helpful.
Not as complicated as I'd worried that it might be, but then it's still not going to be easy.
Maybe I should just forget about making another 1.29.4 release and start the final merge with 1.30.
[edit]
Of course there are other options. We could use a third party GUI package.
Agar, for instance is free, BSD licenced, and looks pretty slick. Downside is we'd need to rewrite pretty much everything to use it, and that could take quite a while.
Or we could just forget the whole thing, and go back to ragged lines of proportional text