Personally, I subscribe to the podcasts of: Sam Harris, Conan, The Energy Gang, Dan Carlin's Hardcore History, Wait Wait Don't Tell Me, and a couple other NPR shows. None of my podcasts, IMO, are decreasing in quality, nor would I expect any of these groups to sell-out as they are off-shoots of other things.
The podcasts I listen to are intentionally hand-selected over time to be 1) informative, 2) have a decent content:fluff ratio, and 3) enjoyable. I unsubscribed from Star Talk because about 90% of it was non-scientific chatter or ads, even though it was enjoyable and informative (sometimes). If a podcast doesn't cut to the damn chase like NDT's, that's an instant unsub from me.
In particular, I find independent podcasts like Sam Harris or Dan Carlin to be FANTASTIC, and that content is free for all to download in multiple ways. So, I'm not worried in the slightest.