"Xenophobic?" Aren't we really just talking about fancy formatting here? How did xenophobia find its way into the conversation?
But as to the real question, there are three reasons this is pretty much a non-starter:
1. We try to avoid building vulnerabilities into the Forum, especially with so little to gain (see point 2)...
https://github.com/showdownjs/showdown/wiki/Markdown's-XSS-Vulnerability-(and-how-to-mitigate-it)
2. It solves a non-existent problem. In 5 years, this is the first time anyone has ever asked something like this, so we can't really place a high priority on looking for ways to add something that no one has needed and that.....
3. ... The third reason already addresses - as
@lordmage mentioned, BBcode gives you the most important of the functionality you're looking for.
I know that's not what you were hoping for, but for now, BBcode does everything we need.