First there is a short way around this for more complex tables, just use HTML via
##"" <# html here #> ""##
HTML must be enabled in the config: ##'allow_rawhtml' => 1##.
Second the Wacko Formatter syntax for the table got some changes, I merged from another branch/fork for the next release[*]. But the table syntax needs a revision.
This issue has two sides, one is to add more possibilities like TH and the like - on the other hand it adds complexity (code and syntax). How to meet the balance between what we want and need without rebuilding HTML syntax just with Wiki syntax?
* ((/Dev/NewFeatures/SyntaxForTableHeader Syntax For Table Header))
So I suggest you open a new ticket in the bug tracker for that and we can add a relationship to ((bugs:277 bug #277)).
search for ##// table begin##
For comparison the Wikka Table Syntax: http://docs.wikkawiki.org/TableMarkup