Heads up, it's time to lower the prices on those spells before POP makes them vendor-bought. Godspeed.
Malo, torpor, death peace, winds of gelid and sunstrike are the only "money spells" that will be PoP purchasable... KEI, GSS, Funeral Pyre, etc will still be drop only.
About a week ago, I checked PoK on Coirnav (PoP/LoY) and Agnarr (LDoN). On Coirnav, many of the Luclin dropped spells were available on the merchant, but not all of them. KEI and a couple of druid spells were what I was looking for, and they were not on the merchant. All of them were available on Angarr. So based on way too little evidence, I assumed that the more common spells from 1 expansion ago are for sale, but the rarer ones are not available for 2 expansions. So it looks like you might have 6 more weeks to unload at least some of your spells.