Martin Johnes published a book on it fairly recently (which I have yet to read, but which looks really interesting). What's often forgotten is that the Welsh Not wasn't an English imposition; it was essentially inflicted on Welsh children by Welsh adults
press.uchicago.edu/ucp/books/bo...
I do think it's an important distinction. This wasn't the outcome of a concerted attempt on the part of the English to stamp out our language (though of course some English people advocated for that)...
It was driven by Welsh school teachers who thought that the best future for the children in their care would be achieved by making them into English speakers, and who thought that end justified cruel means.
I think this is important because we Welsh tend, in considering our history, to focus too much on simple narratives of straightforward English oppression. But so much damage comes by much more insidious, indirect routes.