Now that the pre-requisites are enforced and working (so beautifully, too!) would it be possible to add some additional pre-requisites for homebrew feats?

Currently you cannot set skills/tool/weapon proficiencies as pre-requisites (only armor is available for 'proficiency' type) which I think would be incredibly useful. It would also be great to be able to use level or class as additional options. 

This. All this. Levels, classes, skills, tools, the works. Especially since the greater dragonmark feats have level prerequisites.