"The custom element type identifies a custom element interface and is a sequence of alphanumeric ASCII characters that must match the NCName production and contain a U+002D HYPHEN-MINUS character."
So HTML already tries to avoid the dash in new elements (because it's ugly), but the same might not hold true for SVG or MathML. Are SVG and MathML on board with never introducing new elements with dashes?
Tab stated on behalf of SVG WG that they're not doing dashes. I will ask Math WG folks.
One of Math WG co-chairs chimed in: http://lists.w3.org/Archives/Public/www-math/2013Nov/0020.html
Even though this is his personal opinion, he does state that the group has no immediate plans to add new elements.
I am going to say that since we're now on the WG's radar, we can safely close this bug as fixed.