Well, I would say it's not directly an "upstream", it's a bit more another "downstream" from Xen and XAPI project (at least that's the idea).
It's far too early to answer about XenServer, plus the fact I'm not in Citrix board 😉 So I can't tell. I know it's generating revenue, so as long there's money, things won't disappear into thin air (support contracts and so on).