Its nice to see things that normally have to be written out in a text editor have a nice simple point and click interface like this. Are there other projects like this youve had in mind?
Not right now, although the experience of building this made me realize that most *INFO lumps could probably be represented in this way. I do think in the future it may be possible to have a text file input specification for an *INFO-style lump that automatically creates a GUI like this one. But I would need the lump authors to buy in on the specification idea and format to make it realistic. And that is maybe not possible.
The main reason it's tricky to build a tool like this is the rules can be arbitrary, and they overlap and contradict each other. If it were as simple as "ask the user for a graphics lump", that can be automated. "Ask for a graphics lump, and if you didn't supply one for these other fields, or if any other field is not valid, suddenly the graphics won't show up for any of the fields" is not so easy to automate.
There are also a lot of bugs in the UMAPINFO implementation that have to be worked around. You could ask "why not fix them," but in many cases there isn't much desire to do this. I have had a bug reported and a fix written for over a year but it won't be merged because it requires some compatibility changes (which, admittedly, I am not going to write because I suspect they wouldn't get merged either and I do not want to waste my time). Plus there is this odd thing where users start to depend on the broken behavior and get upset when you make changes.