I agree that "libre" does not roll off the tongue well. It's a rare pattern in English, shared with words like cadre, timbre, and macabre. Those are nouns, so they're not followed by another word in the same way as e.g. "libre software". We have other words like theatre or acre or lustre that we pronounce as if the e and the r are switched. That could work for libre, pronouncing it like "mediocre" (the only other adjective I know of that is spelled that way).

Libreoffice rubs me in a particularly wrong way, because until someone explained it, I did not know whether it was "libre office" or "lib re-office". Either one is strange (the former especially awkward because of the two vowel sounds back-to-back).