And it's worth pointing out that there were many regional or localized gods that were never documented so well as the classic Norse Pantheon that we are familiar with today. It doesn't seem implausible that there may have been a deity that was lost to time and only scarcely preserved by Bede's account.

Yes, it's absolutely possible she's a local goddess. Actually, I think if we accept Sermon's argument that the Germanic name for the Christian holiday is borrowed from the Anglo-Saxon makes it more likely, since it points to the name being less widespread in earlier times.

(That said, we do know the term was a little more widespread than just Bede's Northumbria, since we get the modern term from a different dialect.)

Bede's accounts can be puzzling and raise more questions than answers. But there's also nothing conclusive to suggest he is wrong about Eostre being a goddess. And given his apparently biased views against pagans (understandable for the time), it seems unlikely that he would be willing to attribute the name of Easter to a pagan goddess unless he felt sure of it for one reason or another. Don't you think?

I don't think he was taking a wild guess. It was quite likely the real name of a Pagan holiday, in honor of a goddess; the point of contention was what her name was. I just think that somewhere in the chain of oral transmission of lore about how things had been prior to Christianity, the names of the festival and the goddess got conflated, and that Bede accurately reports what was believed in the tradition he grew up with. Similarly, I don't think Haligmonath involved any actual devil sacrifices, but it probably was a sacred time in the Anglo-Saxon religious year; interpreting Bede's mention of devils as being about the old gods is not something anyone I know of questions. There is a veneer of early Christian folk transmission between Bede and the Paganism he describes; I side with the scholars who think the mention of a goddess who happens to be named Eostre is an example of this.