Never heard of them, but the exploration of the ruins of a long-dead alien civilization is something I would pretty much always love to see, even if I am partial to the post-human scenario. So these Iconians are much more interesting dead and gone than if they were discovered alive. Besides, with the rate of advancement in Star Trek, they would be near Q-like, and I am not very fond of Q-like species. Neither is likely to happen anyway.
Although... With the deep-space mission, setting a totally unrelated story in the ruins of their world might just work. Sounds even more suitable than Qo'noS for creating tension.