I think then it would not only apply to ‘geometry’ to all datatypes listed here: http://dev.mysql.com/doc/refman/5.6/en/spatial-datatypes.html
There will need to be some logic, so that the option for creating a spatial index ‘greys out’ for indexes on non-spatial datatypes, so it is a little bit non-trivial to add.
Also I really don’t know if multi-column spatial indexes aoe possble, so also some reseach is required. This is not somethng we know very much about.