Lopped Austria off the itinerary

Pontresina to Muerren will eat up a whole day, 6 1/2 hours minimum with at least 6 changes and will include back tracking all the way to Zurich. With 10 days, you might want to restrict yourselves to either western/central, or eastern/central Switzerland. Easier logistics. There will be plenty of cogwheel trains either way. Try to keep location changes to 3 to 4 hours.

I agree with Sam. 10 days just isn't enough time to see this much of Switzerland and you're going to eat up precious time trying to include Pontresina, as it's really not convenient to anywhere else on your list. If hiking is your priority, I'd strongly recommend pushing your trip back to mid June. If you go in mid May, many mountain & hiking options are not going to be open.

With 10 days you might consider Murren 4 nights > Luzern 3 nights > Appenzell 2 nights (airport from Appenzell) or Montreux 3 nights > Murren 4 nights > Luzern 3 nights (airport from Luzern).

Thanks for good suggestions - am rethinking Appenzell just because of logistics. Is there another small valley/village we might consider that would be similar. I want to see cows & flowers- ha!

Could you fly home from or to Europe thru Milan ? You could train to Tirano (?) and get the Bernini Express there .

Actually, Appenzell-Luzern is pretty easy. There is an hourly direct train from Herisau to Luzern called the Voralpen Express that takes just over 2 hours. Herisau is 30 minutes from Appenzell on a local train. Sued Ost Bahn is promoting the Voralpen Express as a scenic train ride that bypasses Zurich.
https://www.sbb.ch/en/leisure-holidays/trains-boats/panorama-trains/voralpen-express.html