I see a lot of Clowns & Pigs - there's even a streamer who mains Pig, and does very well with her. I do admit I don't see a lot of Plague players, maybe one a day if that.
There is no Cross Progression between some platforms and we cannot guarantee that this will ever happen. Currently there's cross progression between Steam & Stadia with Switch joining shortly. But as for other platforms this is not confirmed that it will ever be able to be implemented.
These were given out for a short period of time only due to a bug, that bug has now been fixed and the cosmetics removed from those that were not supposed to have them.
We always said that these items would be available in store after a period of time - they were never "rift only exclusives". And they are currently available for shards, not cells so that's not a financial issue.