Is there, or will there be a 64 bit version of Directory Opus?
I sure hope so 
but what's the point? Opus works fine on Windows 64 - apart from the usual issue with DC on the desktop which Microsoft break with every new OS. If we spent a month re-writing the code for 64 bit I doubt you'd see any difference!
The 64bit edition of Windows is so heavily entrenched with 32bit DLLs that it'll be years before its worthwhile for small companies to spend the time doing so. That's not to say that going forward code shouldn't be written to be 64bit clean, but it shouldn't be a primary goal. Wait for Win64 to sell more than five copies and then see.
Personally it would be much better for the DOpus team to investigate some of Vista's features.
Damien