Whether or not the topic title /should/ be allowed to contain wikitext, is discussed at bug 57153.
This bug is just to display a warning to the user, that their wikitext will not be acted upon, if they start typing wikitext into the topic-title box.
(Sidenote: Possibly you could use the same wikitext-detection and/or warning-widget, that VE uses? (For which, see bug 49820))
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=57153