The standard URL query-string syntax, supported by libraries in every programming language worth using, uses & and = to construct “key1=value1&key2=value2”-style parameters. URLON completely breaks that syntax: if I see something like

  _table_achievement_column=instance&ascending:true

my immediate reaction is “so there are two parameters, one called ‘table_achievement_column’, and one called ‘ascending’... wait... why isn’t there an equals sign between ‘ascending’ and ‘true’?” The syntax is just similar enough to query-string syntax that it can mislead to someone trying to parse it by eye. And if you’re trying to pass complicated recursive structures (the kind of structures that JSON was invented to describe) through the URL, they’re not going to be parseable by eye in any format.