I'm strongly considering using mythic earth for a setting (which is actually a few months from being published in the system-less form), but one thought is-- how do you link archtypes such as the magus to it? Leave the arcane pool as is? Change it? Also, for shapechange spells, the transform section might do well to make more use of the mutations from the summoner list, s that lets you simulate the traditional "I just sprouted claws/teeth). It may be a bit rough, but in all seriousness, I've looked at every other freeform system out there, and so far, mythic earth seems to hit the sweet spot between flexbility and ease of use at the table.