This doesn't seem like an intrinsically bad idea; things like the GHS hazard pictograms, DIN 4844-2, ISO 3864, TSCA marks, and similar such things seem like perfectly reasonable additions to Unicode(some of them are already there).
What seems like more of a problem is the idea that the Unicode Consortium is out there fishing for ideas. A project of that scope has more than enough backlog to work through; what possible benefit could there be in putzing around internally with ideas for stuff that hasn't been codified by any relevant user groups, standards bodies, experts, national standards, etc? If they think that they have free time for that, they probably aren't looking hard enough at the stew of natural languages and commonly used symbols out there.
The original round of unicode-ified emoji, while puerile and obnoxious, were at least a solid instance of one of the Consortium's functions: the symbols were in wide use; but saddled with a horrible mess of legacy encoding schemes and general awfulness, so the only thing to do was wade in, hand out code points, and hope that the legacy systems could be burned to the ground as soon as possible. Same reason why parts of Unicode have substantial amounts of duplication, single characters that should be represented as composites, and so on; because various legacy standards had to die.
Here, though, there is no obvious existing standard being modeled on, nor any interoperability issue being solved. If somebody wants Unicode to have a picture of absolutely everything; maybe they should go work on graphics format standards.