I just moved all the feeds from dlat shell script into a database of feeds. The no PubSubHubbub and non PubSubHubbub feeds are together in one place. and a couple of duplications are now erased. the non PSHB feeds still get polled but the list of feeds is iterated from a database rather than shell script. This make addition of new feeds simple. All I have to do is supply the feed URL to a subscription script which tests if the feed is enabled for PubSubHubbub or not. If it is a hub subscription is enabled and its work is done. if its plain old RSS it is flagged as such and it is prime for polling twice an hour.
I expect the 15% PubSubHubbub enabled figure to grow. The genre using it most are experienced podcasters with some broadcasters like CBC using it. all but a few of these are enabled using feedburner which is the easiest way to get enabled using its pingshot service.
I think real time subscriptions alerts without polling will come into its own when audio segments are frequent and of a time sensitive nature like news or comment in audio reporting or audio bloging.