I think that Mentor, or any of the major ECAD companies for that matter, will not fully support IDF 4.0. There is too much ECAD database information embedded in the format. This would lead to a universal CAD database transfer method that would make it too easy to move from one ECAD vendor's software to another's. Since the IDF usage is to check the PDB for interferences with the enclosure I would not look for IDF 4.0 but a continuation of STEP or ProSTEP as the improved ECAD to MCAD interface.
One could make the same argument about Gencam, GenCAD and ODB++ but those formats drive real downstream tools that companies use for manufacturing PCBs. ECAD software companies are stuck supporting them. Otherwise we would have ASCII auto-test files and pick & place files with for Gerber photoplotter files and NC drill files as the only output from the ECAD tools.