Good question... I haven't thought about it deeply, but I would say that using this lib itself won't have impact on accessibility: if the HTML fragments are carefully crafted to take accessibility into account, then after HTML fragments swapping the DOM will keep this aspect.

I would say the construction of the HTML fragments (done by the user of this lib) is the most impactful part.

Since the URL can change after a HTML-fragment-swapping with this lib, I can imagine that screenreaders will detect the URL change and take the new layout into consideration, is that right?