We might also implement rx:meta-info instead of forcing users to produce fox:meta-info or rx:meta-info depending on their intended FO processor.
Fiddling with other people's namespaces is considered unpolite, at least. They might not like this.
Processor specific extensions are just that: processor *specific* extensions.
There has been an EXSLFO initiative (search on sourceforge) in order to get some extensions standardized, similar to EXSLT. AFAIK nothing has been coming out of this, yet.