XM takes U-Pop down every now and then to make way for specialty programming like Holly and short-form programmed specialty channels. I'm not sure if it is on the Satellite right now or not, my XM radio isn't able to get a signal right now.
I hope that BBC Radio 1 survives, rather than UPOP in this situation. I love alot of the specialty programming on Radio 1 (daytime programming, dance programming, the weekly countdown, etc.), even with the amount of DJ chatter. I would be very sad to see Radio 1 leave the Sirius lineup, though I think Radio 1 will survive the channel merging coming up.