This is a teeny weeny bug, probably related to :discourse2: being bespoke or something. It would be nice to have it in the default emoji sets though in other instances. We like and refer to the mothership quite often!
FWIW, I find this idea appealing. I just tried a workaround of adding it as an image instead, but that got pulled out as the onebox thumbnail so didn’t really work as well as I’d hoped.