Grey / default blocks for missing textures are fine - nothing wrong with that. The problem is we can't count on a consistent range of blockIDs being kept open for custom textures/blocks. Another problem of course is currently the game is crashing with custom blocks. The attempt at having the launcher download custom block packs from servers was maybe well-intended, but not successfully implemented. It hasn't worked for long enough that the devs should have either fixed it or taken it out. At this point, it's best to just let us players handle making and installing and distributing our own textures and blocks. I don't think new/different textures should be a priority for Schine devs right now.
When players customize or mod, and are then frustrated by spending more time re-tweaking their files after updates than playing the game, they just quit playing, or downgrade and go offline. I've heard this dozens of times as players rage-quit after updates.
...and poor plusnine, he wen't probably farther than anyone ever has into making really nice custom blocks and textures, and despite some support from kupu, he eventually became absolutely frustrated and stopped. I'm not sure he even plays offline anymore. It's sad. I was on teamspeak with him and others quite often to witness his frustration while he was making (and re-making after updates broke it) his pack.
But back to the topic standard hull, and "new textures"... standard hull could even be accomplished with 1x1 textures, and they're great the way they are now as a seamless, solid color. It's quite useful in designs. Again - new / different hulls should not be a developer priority right now, imo. Core elements of gameplay have been missing for 1-2 years or more. We need that before we need "new shinies".