I'm going to be submitting an update for libmodulemd today for all released branches of Fedora. This is *technically* in conflict with the Stable Updates Policy, but it is both necessary and should be safe to accomplish.

1) The teams that were planning to switch to it from the previous python-modulemd have not yet done so or are just starting to, so it's not believed there is anything currently running in production with the older version.
2) The API is *source*-compatible, but not binary-compatible (hence the soname bump), so it will just require a rebuild if anyone *is* using it.
3) The reason for the API change is that certain semantics around ownership of memory have changed. This mostly impacts the GObject Introspection bindings for other languages such as Python, but as it technically changes the ABI contract, bumping soname was the correct thing to do.

[f26] https://bodhi.fedoraproject.org/updates/FEDORA-2018-f731883394
[f27] https://bodhi.fedoraproject.org/updates/FEDORA-2018-a1c9076f1f