Where are they?
Well, really that is a question for the first two, as FoP is Flask of Petrification, which is just a waste of reading now.
But, in TWW, we do not have those at high levels to use any more. They are all exist for low level use, but not max level play since TWW began.
Is there any plan to bring these things back for high levels?
Doubt it.
Nets are a lot less relevant when every class has MULTIPLE means of CC.
I don’t know what Stealth Kits even refer to (googling it literally returns this thread as one of the top results), but we have Invis Pots and Rogue Shroud for max level use.
FoP was nerfed to be a minor absorb potion ages ago (as the WoWhead comment put it, it went from DI in a bottle to Power Word: Shield in a bottle) and is therefore irrelevant. The un-nerfed version is entirely broken and would break a lot of encounters, I’d imagine.