Accessibility: podcast subscriptions can’t be added using keyboard only
As of 3.*, the only way of adding a podcast subscription is
to browse through the Playlist panel, hover on “Podcasts” and
click the “Plus” icon. That icon is not accessible using the
keyboard (neither Tab, Alt nor the arrow keys will help); it’s
not even broadcast through the at-spi bus.
To make things worse, that particular feature is not accessible
through any menu command or keyboard shortcut. The only thing
that remotely resembles it would be the Network feed dialog,
i.e. Ctrl-N, which does allow you to read a podcast feed (but
doesn’t provide an actual subscription).
The 4.0 interface has revamped a lot of stuff, but is of no help
so far (AFAICS) with regard to podcasts. See also #22168.