Well, at last I have come back to working on this. Haven't gotten much done yet, but I made a new mist fro which is the equivalent of summon monster for the ethereal magic. This mainly involved making a new template for creatures made of mist. Haven't done the later iterations yet, mainly as I'm as of yet still uncertain if it should be a level 1 or 2 mist form. Also the template may or may not need work.
As for the ethercaster. I'm as of yet uncertain how I should replace the Sustaining Shadow ability that the shadowcaster grants. For those unaware, the ethercaster is heavily based on the shadowcaster as they both deal in using magic powered by transitive planes. For this reason most abilities granted are intended to in a way mirror those granted by being a shadowcaster. As it is, I am uncertain if I should just rename sustaining shadow, or make some other set of abilities as they get closer to the ethereal plane (such as a miss chance, reduced fall damage, chance of ignoring critical, etc.). Suggestions would be welcome.
Also not sure if I should grant bonus feats like a shadowcaster or replace that as well.
Anyone with ideas for a mist form feel free to let me know and if it seems to work I'll likely use it.
Also, for those that may care, I received permission from Roland St. Jude prior to reviving this thread.