Composr development update - January 2017

I can't recall if you've said this elsewhere, but will the upgrade to v11 (from v10) be relatively easy? This post is almost all about v11, even though v10 is still in the Release Candidate stage. Several of my websites have been using v10 in production for a while now, and I've done a lot of customization to their themes, mostly in CSS and templates. On a scale of "seamless migration" to "might as well start from scratch," how much work do you think it will take to bring my sites over to v11 when the time comes?

As always, I really appreciate what you're doing! Thank you for keeping this awesome software open-source!