Are Ace headphones like Sonos speakers?

Not at all, no, if you read any of the many threads in the headphone area of this forum. Essentially, they’re excellent Bluetooth headphones, with an extra feature that connects them to certain soundbars that Sonos makes. 

To add to ​@Airgetlam summary of the Ace headphones, the new Ace Ultra is available at the end of the month.  Unlike the original Ace, the Ultra model can bind itself to a Sonos room, allowing it to link to the audio playing in that room, basically piggybacking on the nearest Sonos room and playing the audio on the Ace Ultra instead of on the room device.  That’s not the Ace Ultra being its own Sonos “Room” (the WiFi and processor needs for that function aren’t conducive to a headphone), but it is close.

Doesn’t this mean that the new Ace Ultra can act as it’s own room via WiFi?

“Don’t have anything playing on a speaker and just want to play to your headphones? Simple: go to the System tab in the Sonos App, select your Ace Ultra, then find and play content the way you normally do.”

My take is that it’s not playing in the speaker it’s linked to, just the headphones. ie, you can’t also play it in the linked speaker. So not really a separate “room”. I could be wrong, I haven’t seen it yet.