[selfhoster11]

If your application interfaces with ReiserFS directly (fsck/servicing scripts), or you expect to see certain performance patterns (like high speed on lots of smaller files), then I would consider this userspace breakage.

[djur]

In the same sense, Linux broke userspace for 386 users in 3.8 because the users expected Linux to run on their computer. An optional build-time feature being removed does not break userspace.

[selfhoster11]

Arguably yes, abandoning an architecture is breaking userspace. At least for those that are still using it.