I've also gone through this process and evaluated Firebase, Realm, Pouch/Couch... They all ultimately fall down at some point and you end up in a situation where you have to build some strange hybrid with a separate API to do the features that aren't supported, and you can't really use them as full MBaaS like you'd hope.

Send me an e-mail from the info in my profile, and I'll include you in the alpha test! I would really appreciate some additional feedback.