BUR #57935 has been approved by @evazion.
deprecate alternate_design
deprecate official_alternate_design
I can't think of a single thing this tag is accomplishing that our numerous "alternate" tags aren't already doing. Namely alternate costume. The additional line about speculative designs for unseen characters is already covered by design speculation.
We also have redesign which is largely mecha and can accommodate non-human and objects.
Also related to forum #377735 which I similarly still find redundant with more specific tags. But at the very least is a larger established dumping ground.