I put that in quotes since obviously nobody really knows what real aliens actually look like. What i mean is, aliens that clearly are not human actors with styrofoam on their heads speaking english.
Do you feel the fans would accept that, something that communicates but does not speak, not at all human, maybe corporeal maybe just light. We've seen such things on Trek, the Medusans, The Companion, the shimmering thing that made the humans and klingons fight, Redjacks true form etc but they still had to influence something bipedal and then we learned of their intents through the people.
It would make for slow storytelling, first contact would take months instead of an episode which would be a nice change in itself. I would just love to see Trek do more than endlessly project 20th century political and social issues in the "future".