The long going effort of Making Puppet optional is coming to an end and there is a PR  to extract all the puppet code from core to a plugin. I hope it gets merged soon and IMHO it is a good reason to bump the major version of Foreman. Therefore I propose the next release would be 3.0.
Although I think it is enough reason by itself, we can still have some other major changes included. If you have any thoughts on what other backwards incompatible changes we should make in this release, please come forward as soon as possible so we can discuss those in time.