How to lose readers of your syndication feed
It's pretty simple:
- change your syndication feed URL
- but don't remove or redirect the old feed, just stop updating it
- and don't put up an entry about it (visible in the old feed).
Readers who are not especially attentive may not notice for weeks, only vaguely wondering if you've taken a vacation or something. Especially if they read a fair amount of feeds and are behind in their reading.
As far as I've gathered, most feed readers are perfectly willing to have the feed format change out from under them, so there's no real reason not to redirect old feed URLs to the new canonical one. If you have mass quantities of automatically generated feeds this may be a bit challenging to do, but most things with feeds just have one or two.
(In theory a permanent redirection should even cause feed readers to update their internal memory of where to get the feed from, but I'm willing to bet that that's mostly honored in the breach.)
In my case, the only way I noticed was that someone else linked to an entry I hadn't seen on the blog in question. When I clicked through to read it, assuming it was an old one, I happened to notice that it was actually a recent entry, and that set me to wondering why I hadn't seen it in the feed.