Put a hollow stretched canvas painting over it. Who cares what it looks like?
I just think that designing hardware to fit within another piece of dead hardware just to achieve what can be done off the shelf for $50 is not really my idea of a fun personal project.
Different folks different strokes. But I think saying "who cares what the decor inside the house looks like" is a little naive. Surely you can imagine that there is some population of people that care what the decor inside their house looks like AND do not want to hide the display on the thermostat? I think that group of people is probably a significant number of people... large enough that you are not raining on OP's parade.
I chose the CT101 based on low price, you could get a Honeywell T5 which is much more aesthetically pleasing and still supports Z-Wave, which accomplishes the goal of having a thermostat that won't lose smart home cloud support (by integrating it with Home Assistant using the standard Z-Wave protocol).
Plenty of cheap thermostats have good aesthetics. The $30 round Honeywell analog thermostat is a timeless design. Their $30 non-programmable digital thermostat (RTH5160) is aesthetically pleasing enough, I certainly wouldn't call it ugly. I didn't interpret the stated goal of this project to be particularly relevant to aesthetics.
Someone else replied about how ugly most cheap dumb Z-Wave thermostats are. Nests are beautiful by comparison. I've been searching for something I like as much aesthetically and come up short. That's one of the motivators
Solves the problem permanently, no risk of future deprecations.