Onlines services sadly was one of those things that if it had taken traction could have been so much better than what it was. With what was offered, it relied upon whoever was providing the service to make use of in-winamp hooks so that the integration of clicking links, etc could work without it opening in an external browser (as the post-sale shoutcast view now does).
So technically there's nothing to stop anyone making a new service (one of the things for the 5.66x releases was making it possible to manually add services if wanted if the main website went away - as happened). The big issue is there wasn't too much documentation on how to do it & a lack of interest in general now.
With the specific case of podcasts, the service that Winamp used (as it was a Winamp provided online service) doesn't exist anymore however you can still add feeds to Winamp from any of the feed aggregation sites but there isn't a good way to do it directly from within Winamp (or WACUP for that matter).
With WACUP, if there's an interest then I would consider adding in some sort of native view or a way to search for feeds from a service if any of them allow for that (I've not looked so I don't know for certain if that's even viable). That would be more useful than trying to implement something with the online services plug-in when personally I'm looking to see it dropped from WACUP installs (it doesn't really offer anything of use as this thread raises) and having things contextually together within their parts of the library, etc are better from a usability point imho.
So if there's any suggestions on podcast services that are ideally free & allow searching within them via an API or simple request that people are using then I'd love to hear about it

-dro