We have merged a breaking change (DB API) in develop, so it will now become version 12. If you want to stay on version 11 please move to staging branch.
cd frappe/frappe-bench # or your bench path
cd apps/frappe && git fetch upstream && git checkout staging && cd -
cd apps/erpnext && git fetch upstream && git checkout staging && cd -
Version 11 is still open for new features, so you can open pull-requests for new features to the staging-fixes branch. Breaking changes can go to develop branch.
If you are following the forum, there is really no defined roadmap. We try and follow Semantic Versioning (semver.org), as per which any breaking change results in a major version release. Since version 11, is on path to stability there won’t be any more breaking changes in v11. (Non breaking new features can still go)
Re: upgrade path, there is always an upgrade path in ERPNext!