People try to do that already. It kind of ends up like pic related.
>>2913705t
When we sete that we usually ask people to cut it out, and if they don't, or especially if they're abusing PMs like
[@Background Pony \#0F89](/forums/meta/topics/feature-suggestions-and-discussion?post_id=5388089#post_5388089) described, then we start banning them.