Because of the solid architecture of eDirectory and IDM, scalability has never been an issue on 32-bit eDir & IDM. That said, Currently 64-bit IDM 3.6 is not yet publicly available. 64-bit IDM 3.6 is definitely on Novell's Roadmap. 64-bit eDir is a step towards it.
Supported version of 64-bit IDM 3.6 should be available on several platforms in first half of 2009 unless priorities change.