Atom is widely used (when you see "RSS", it's often Atom). And in any case, outputting the data in an extra format takes barely any time.
As for PubSubHubBub, all they have to do is add a tag to the feed with the Hub's url and send a POST request to the Hub when the feed has updates; that's it.
For the effort is takes (or should take, assuming they have a decent architecture), and the advantage of being automatically compatible with a bunch of existing applications, it'd seem strange not to do it.
I had a reply, but I lost it due to session shenanigans, and I don't want to write it all again.
But for RSS applications: considering they already have more than 14000 Twitter recipes, supporting IFTTT seems an excellent reason for implementing RSS. Particularly since it should take a few dozen lines of code, if that, in any decent language.
As for PubSubHubBub, all they have to do is add a tag to the feed with the Hub's url and send a POST request to the Hub when the feed has updates; that's it.
For the effort is takes (or should take, assuming they have a decent architecture), and the advantage of being automatically compatible with a bunch of existing applications, it'd seem strange not to do it.