Void elves would have my vote.
1. They'd easily make the coolest forms and
2. Druidism in wow is an elven thing, it's just weird, no other elves can be druids, but all the other horde races can? At the very least void elves should and if they want it to go further, then humans. But void elves before humans.
3.the druids desperately need help with the nightmare thier knoweldge an d methods could greatly assist and produce this new race/class combo.
Lore wise - it could go something like this: the void elves have been very interested in Elune's dark moon powers and Tyrande's control over it has even won some of these Thalassians back to Elune worship, it's caused a boon in the void elf priest population, as working relationships strengthened first with the Highborne, then the Priests black moon sect, the druids seeking means to control or remove the nightmare, have sought the void elves' help.
Totally up for investigating htis, many void elven botanists have teamed up with the night elven and worgen druids to solve the problem, these void elves have learnt and adapted the void to nature, increasing Azeroths defense against the void as well as increasing effectiveness against it. The void elves have learnt to master more of nature this way and some have joined the Cenarion circle as void druids. They hope to train Azeroth's to res