I don't know. It's technically possible, and there is really no super compelling reason why not (it would be nice to be able to put signs on doors and in corridors. signs that don't look like a ghost spray-painted them with ectoplasm). Allowing players to press "r" on a hull or door block and add like 32 characters with color and good size variation would allow a lot of additional atmosphere/decor and ability to better detail directions and instructions for many things in-game.
I think the main issues are 1) there are fundamental gameplay issues, major bugs, and major features all constantly being patched and updated and that takes a far higher priority, 2) since it's possible to make crappy signage using displays or write crappy big signs using whole blocks, the priority on being able to add decorative text to non-display blocks is reduced even further, 3) I'm guessing that some people think allowing signage on non-display blocks would eat up too much memory, although in fact it ends up the same if you instead add more display blocks to achieve the same result (but in a horribly-looking way).
But mainly it's about #1:
Entirely new planets are incoming.
Entirely new power & systems are incoming.
The entire galaxy generation and resource distribution system is being overhauled.
Fleets are still buggy-tech.
Player advances in docked hull, docked power, and non-colliding block compression (lamination) through docking technologies have completely diverted the combat meta into a dead-end line of "technologies" that rely entirely on bugs and yet cannot be avoided or you will simply be destroyed, not to mention the way all that over-docking seriously destabilizes multiplayer servers.
There's so may more critical issues besides these that it is hard to keep track of them all. They all take priority over painting blocks for a game in this stage of development. That's kind of a 'finishing touches' sort of thing.
