Re: species that can be crossed
I grew sikkimensis just outside Portland, Oregon at about 700ft elevation for a number of years before moving. I only lost the p-stem one year when I didn't protect it very well, but it came back quickly. All other years it did fine.
I wish I had more appreciation for what I had at the time.
For all I know, it might still be there.
I still get the impression it isn't the easiest plant to find, even in the states, and I suspect what, if any, circulating specimens are around are from seed fairly recently - which I have had no luck germinating - and, as you mentioned, may vary in temperament.
However, this is the place to find such things so hopefully a source with a good, tested hardy cultivar will come forward.
Keep us posted.
Who keeps calling me nuts??