ductless HVAC recessed wall units

I am considering having ductless HVAC installed in my early 1900's house. Initially, the recessed ceiling cassettes looked very promising due to them being "out of the way" unlike the standard wall units which are hung on the walls. However, I was told by the contractor that the ceiling units aren't as efficient as the wall units. Also, the ceiling units wouldn't fit into the 2nd floor ceiling as the joists aren't deep enough for the ceiling cassettes without them protruding through the attic floor. This leads to my question:

Is there any technical reason why a manufacturer has not made a recessed wall unit? It would have to be limited to 3 1/2" interior depth and 14 1/2" interior width to fit in a standard 2 x 4 wall with studs spaced at 16" o.c. The height of the unit could probably be several feet to get all of the components in. It would be great if when this were installed, all that would be seen is a grill and flange.

I wrote to a manufacturer about this issue and have not heard back.

Is this such an unusual idea?

Does any manufacturer make such a unit?

Any insight into this issue would be most appreciated.

D