First, does the tag seem reasonable? Alternatives seem to be tagging netflix + cassandra.
Looks fine to me. A technology deserves its own tag.
Then, which tag to choose? priam, netflix-priam, cassandra-priam or even something else?
I would name it priam, as I suspect that is unlikely to be ambiguous any time in the near future. We can always create synonyms if people insist on tagging with something different.
As Robert suggests in the comment, please take the time to write a tag wiki for it (or at least the excerpt) to help people know to select it.
If I do create the tag, should I proceed to tag the old questions with it?
That would be great!