I've been working lots on glom, my databases-for-the-rest-of-us application, and I'm starting to believe again that it's viable. I had a kind of epiphany – I found a suitable set of user goals to discard so that I could actually target one of the sets of user goals. So, glom will not be able to edit and redesign existing databases. It will only be able to edit and design databases that it created from the start. That means it can deal with a far simpler set of database field types. That makes the whole thing more usable anyway.
I've also realised that it's kind of stupid to make the UI for designing the database structure look like the UI for editing the data in the structure. I'm not sure what the best UI is, but it's clear that I would have been better off just cloning the FileMaker UI from the start. So I'll rework the UI after I've got some of the basic functionality implemented. The code is a mess too, but I think I see how to clean it up so that it's worthy of patches.