What also worries me is that I am using a 'connected device' arrangement with a WDTV and some of the difficulties over time with this have been described here (10003 error).
I have to have this Sling to WDTV feature work. It can't be removed in a future product 'realignment update'. to service or features.
So given the kneecapping of the 500, I think it is reasonable to assume any and all functions on other Sling products may also be short term.
It's a rock and a hard place no matter which device you own and it makes me wary of suggesting Sling products to others unless there is a statement here of ongoing service guaranteed.
The following article will explain why the "My Media" feature is no longer displaying on the SlingPlayer applications:
Sling Media Moderation Team