This is going to be interesting - most headcanons have English language encoded engramatically into the fluffy’s DNA, but the approach you’ve taken is that just language capability is encoded, rather than a specific language.
Good catch that learning can start during pregnancy with the foetuses learning their mother’s Mummah Song, although removing that could potentially affect other developmental aspects like socialisation and bonding (again most headcanons have babies learn their mother’s Mumma Song, so that they can be found by the mother in a herd or fluffpile of multiple families), which would affect the language experiment.
Another author, Oculusfluffy, wrote an entire series about fluffspeak being an entirely separate language in their Fluffspeak Nation stories, much like Jamaican patois.
I’m trying to work through the series, but it’s a bit dry for me, and a lot of behaviours and plot progression appears odd, unless you’re familiar with Singaporean culture.