Useless BANANAS!!! (nanab berries)
Niantic should change these berries to give 2x stardust. Their function doesn't really work anyway, unless you wait. I would actually use them if this was their purpose
Answers
Some upcoming event will probably involve some sort of double stardust just like they did in the fall. It will happen soon enough.
But berries for double xp and/or double stardust won't happen. The current berries are all mon specific, ie
"stop this mon from moving"
"Increase my odds of catching this mon"
"Double the candy for this mon"
I'd like to see to berries for
"increase the IV of this mon (if I catch it) some RNG amount"
"increase the lvl of this mon(if I catch it) some RNG amount"
From my experience when using them (which isn't often), it seems that Nanab berries only prevent a Pokemon from moving, and not hitting your Pokeballs away.
If that is the case, Niantic could make it so that it also stops the Pokemon hitting the ball away which might increase the use of the item.
I still dump all of mine though, I only use them if I happen to get some from a Pokestop I've just used and some low level Pokemon spawns or something.
I'm going to throw it away anyway and I'm not going to use a Pinap or a Razz on a Pidgey, so why not use it.