Peter, subtome.com AFAIK just redirects you to a RSS/Atom reader and such buttons exist for ages. Even me wrote universal RSS reader cliws.com several years ago ;)

#RSS is dying and I prefer #IndieWeb h-feed because it's part of web-site instead of an invisible XML.

#RSS is dying for an simple reason — it's one-directional publisher->subscriber technology. With rise of social networks with their P2P communications RSS is really "walking dead" if we talk about human-to-human communications. RSS still used for one-directional public updates distribution.

The 'Subscribe' button I miss should allow to subscribe to an private h-feed (like family or company feed) and allow bidirectional communication: I should be able to send comments to feed's owner and receive replies back.