IMDb gives no credits for Felicity Kendal after 2008; it has the new version of "Upstairs Downstairs" beginning in 2010. It's still in production, apparently, so Felicity could still show up.
(She didn't appear in the original "Upstairs, Downstairs" either, again, per IMDb.)
I've watched most of "Downton Abbey" but find myself feeling irritated about the ahistorical bits. Not so much the table settings (on which I'm no expert), but on the unlikely emotional connections between the Upstairs people and the Downstairs people. (They really CARE about each other...which seems inaccurate for the period.) "U,D" got closer to getting that right, I suspect.
I'm still excited about my first book being up on Amazon (about online forums)!