I think there are many speakers that have the capability of "disappearing". However it seems that a certain degree of "invisibility" is dependent on the complete chain of recording from the studio all the way to the listening room.
Some speakers may disappear, move em and they're back or change the source and they're back or change the recording and they're back...
Well, you get my drift.
After saying all this, if all is optimized, it seems that planar speakers seem to be the easiest to make "disappear" followed by smaller monitors then narrow baffled, well braced floorstanders with quiet enclosures.
The issue is whether you can make a *particular* speaker disappear in your room and not have a "disappearing" speaker (since basically NO speaker can just disappear on its own).
Good Luck on your speaker hunt!