I've been working with one other XF member here on creating an add-on that uses Cloudflare and basic common sense to either moderate or reject potential spammers and so far it is working with great accuracy.
I will not be releasing this publicly for two reasons: 1) I'm tired of supporting the lowest common denominator here (sorry but my time is valuable these days) 2) anything released publicly is just going to be subject to spammers also getting ahold of it and dissecting it.
The good thing about the second reason is that, at least in my opinion, the major feature that is preventing registrations are something that I don't see them being able to get around very easily.
We will provide a private release on a case by case basis for a fee with the understanding that we are developing this first for ourselves and secondly for you. So any conflicts on your site that can not be reproduced on our sites will be a low priority. It's ok if this isn't acceptable to you. You don't have to buy it.
So, I was just curious who all uses Cloudflare and would be interested in something like this? We aim to keep it simple configuration wise but it will be very powerful underneath and give new options to stop new registrations and those that do get by will face more obstacles, all while keeping legitimate members happy and positing with no interruptions.