As noted by Buzby, integrated support for 32-bit integer would require significant change to the PICAXE firmware, compilers, PE6 and simulation, and likely would require an entirely new PICAXE range of devices.
For those cases where 32-bit integers would be useful it should be possible to create macros for the operations required which likely would work for all existing chips. There are some examples of doing 32-bit maths on the forum and help is likely to be available through the forum for solving specific problems.