I have an interest in helping out. I've created opentype.js, an OpenType parser and generator (https://github.com/nodebox/opentype.js).

I understand your concern for keeping the format declarative, but I'm not entirely sure you can handle TTF files that way, as you'll run into walls very quickly.

For example, to know the number of entries in the `loca` table, you have to parse the `numGlyphs` field from the `maxp` table. The `maxp` table doesn't have to come first...