The sheer number of potential promotions is quite large and so far I'm considering one of these:
Adenium (seems like an interesting alternative to using Hydrangea all the time)
Sedum (seems like quite a good debuffer)
Skunk Vine (as mentioned in posts above)
Bouvardia (lowest prio, curious how the healing ability holds up)

On a not entirely unrelated note - with the latest 2017 ticket, I completed my collection of 5* from that year.
Just shows how much of a pool I'm choosing from.
I'll probably look through other possibilities searching for something interesting.