The proposed use of WKT as the format is simply because we store geographical data in databases (SQL Server & MySQL) in their native spatial types. Both have built in functions to convert these to WKT for output (STAsText, ST_AsText). Other alternate formats (e.g. GeoJSON) don't have built in functions for export.
I suppose if you wanted to make the maps work with GeoJSON as well (if other databases can output that, or maybe if someone just stored it as a string in their DB) then there could be a drop-down to select from the different supported spatial formats. That way, more formats could be added later if required?