Finally got it to work! Took longer than anticipated due to the fact that I had a lot of code from earlier experiments that was actually hampering what was well done.
For future reference, my DataSource class drops the ICollectionView and IPagedCollectionView interfaces from earlier experiments, and now implements IQueryableCollectionView, IQueryable, IOrderedQueryable and IEnumerable (among typed versions of these interfaces and the necessary INotify*Changed apparatus), and has its own IQueryProvider.