Hey T DC, I've had similar experiences but I didn't want to fess up less someone think I was trying to engage in mind fuckery. Glad you did. 

When I first saw ultimate reality (nibbana) I thought it would be permanent but, so far at least, it comes and goes. Probably that's because I haven't had any really clear cessations and I'm still fettered up the wazoo, lost in the middle paths pre stream entry.

By nibbana I mean simply seeing things as they are (and have always been). The weird thing is - so far as I can see - that nibbana is always available but somehow we choose not to let ourselves see it, sometimes for long periods of time. I don't really understand why ultimate reality should let relative reality (samsara-dukha) continue to delude itself, but that just seems to be the way it is. If you wanted to put a theistic storyline around it you could say something like "god lets us suffer just so we can admire him and find our way back to him", but that makes him sounds like a pretty narcissistic mean old man. Also it might give the wrong impression - because nibbana is totally ordinary whereas people tend to think that god is special.

Realized I forgot to answer the second part of your question. Things like seeing emptiness, Buddha nature or rigpa are just experiences as far as I can see - they also come and go and can be seen for what they are - I don't think they are ontologically more privileged than any other experience such as taking a crap or going down the pub, although they can seem quite special for a while before the novelty wears off.