I've gone from a 2x9 to a 1x10 on my mountain bike and it's been great. I don't have quite the same range but it's good enough (I rarely used the super low gearing), but I do have one less derailleur to clean mud out of or worry about maintaining, and I've got a dropper post where my left shifter used to be. So it's great in that regard. I just don't see the same appeal for a gravel bike, where I've ordered a new bike with is 2x10 though because I wanted the extra range and steps.
The only 1x gravel bikes I've seen have been at the lower end of the scale so I can see them being a factor for cheapness/simplicity but I don't think they'll catch on in the same way that they have for MTB. I certainly don't think I'd use a dropper post much on my gravel bike, but I'm guilty of just using it as a more comfortable road bike.