That Extra Race

[Rumil]

Surely the 'sylphs' were just a subset of the Maiar, those who were air-related spirits, perhaps associates of Manwe? The forerunners of the Balrogs and the Sun were fire related spirits. To round out the four elements, I expect Ulmo's friends were the water spirits and Aule's (and perhaps Yavanna's) followers were earth spirits.

Of course as Maiar they would be unlikely to be constricted by these roles (witness the Istari), perhaps an affinity or 'alignment' with the different elements is more likely?

What about Ogres and Pygmies, two races referred to briefly in early writings in HoME? I guess JRRT didn't want to take these any further but these could be interesting possibilities for RPGs or FanFic