> The podcasts I enjoy the most [...] All the podcasts I listen to
Emphasis on "I". You are not everyone, and so you don't control all the demand, and so you don't control the direction that the market moves in. Though it's not self-evident that we're headed towards podcast centralization, I think it's a legitimate concern here.
Social networks like Facebook ate a decent part of the open internet's cake in the 2000s because the centralized services were easier to set up and user for the end users (compared to the RSS and SMTP hacks).
I think that's what is going to matter here: If Spotify does a significantly better job than plain RSS, then they're going to be "the" place to listen to podcasts, and can start building a closed ecosystem and then use their monopoly to rent seek. And like in the social networks case, I don't think it's going to be that hard to improve on plain RSS. Some podcasting apps already have comments, user ratings, etc. and I definitely find this sort of thing useful.
Maybe the path of least resistance in these sorts of situations is always some degree of centralization, but I obviously hope the tide starts going back out at some point - preferably complete decentralization, rather than just federated protocols. I think it's a bit like how native apps can move faster (in terms of new APIs and stuff), and the web slowly follows along, waiting for certain things to be "proven" before standardizing them. I think the web wins in the long run, but native apps end up being the "exploratory" instrument in our search algorithm.