dev-libs/protobuf-3.3.1 was released on 2017-05-13.
dev-libs/protobuf-3.3.2 was released on 2017-06-21.
Thank you for the bump request. You can help the maintainer with further information: Does a simple bump [1] work on your system? Chances are high, because a first look on the bump revealed only small changes. [1] https://wiki.gentoo.org/wiki/Custom_repository#Simple_version_bump_of_an_ebuild_in_the_local_overlay
dev-libs/protobuf-3.4.0 was released on 2017-08-15.
Currently stable ebuild works but need PATCHES to be dropped. @vapier, do we need to keep patch to redirect protoc input/output? https://github.com/google/protobuf/pull/235?
dev-libs/protobuf-3.4.1 was released on 2017-09-15. Version bump is a good occasion to drop "java" and "python" compatibility USE flags which are only for PDEPEND since bindings were split into separate dev-java/protobuf-java and dev-python/protobuf-python packages.
These version bumps have been committed (with updated patches): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=dd8afe0da7b8f9ab41cd4709b32c5deea4c6d8d6 https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=630682554ec205aaa935859a753db69c8549fa45 https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=b24f9cfd6f13efa097e1529084f8c6a1caf29f78