I assume that such per-user options are now clashing with the new page caching optimizations in the mail archive (unlike the rel=next links which can be baked right into the cached page and therefore still work). Since they don't work anymore, it's probably better to remove those features altogether, than having misleading options in the user control panel.
Besides, nobody else seems to need those features. It's not right to burden you and the site with features that clash with its design just because of me.
I really appreciate the effort you've put into those features, but it does look like the drawbacks outweigh the benefits.