User blog comment:Rappy 4187/Technical Update: July 27, 2016/@comment-24473195-20160728152602/@comment-126761-20160728175238

It is currently intentional that it does not parse wikitext (it's supposed to be a brief "hey, welcome to our community" note) - but if there's more fancy things you'd to do with it, we'd be interested to hear about it. (As normal, I would recommend Special:Contact/feedback for suggestions.)

I have updated the help page to indicate the message to edit - but including direct edit links is something we've been looking at. Sometimes we'd rather just get the ability out there in a basic way, though, so people can start to use it sooner.

Interesting thought about providing a special page list though - that general idea has come up before, but hasn't been a top priority since Help:System messages/whitelist does exist.