What I would like to see is the whole OS/2 being converted to 64 bit, although 32 bit would do for a start, I know there is a 32 bit CMD implementation but it needs everything from networking (IPV6) and up with some sort of VM built in to enable use of 16 bit windows applications. In other words I would love to see everything (except the win 16) on the WSeB install CD changed up to 64 bit and then have the necessary 64bit drivers included on WSeB CD2. I know it isn't very likely to happen but I too can dream.
The 16bit Windows (and DOS) applications is the easy part, just use DOSBOX, which is quite capable now of running Win16 and many DOS apps, though it won't give you the hardware access that OS/2 does, nor the shared clipboard.
As for 64 bit, what is the point? All the apps are currently 32 bit and will remain 32 bit. If the swapper back end was fixed/extended, could use PAE memory for swap (already possible) and run lots of 32 bit apps, each using 2GB or more memory, though there is still the shared memory problem.
Personally my fantasy is a bit different then Martins. Start at the bottom end and add a OS/2 subsystem to Reactos. I choose Reactos as it is NT compatible and NT was originally designed to run OS/2 and is more similar then Linux.
Write the backend (Doscalls and a few other basic bottom end DLLs) and use the OS/2 binaries for the PMSHELL and WPS until someone rewrites them. The OS4 guys have already sorta done part of the work, though they don't like the GPL, which is what Reactos is licensed as. Once the bottom end is done, you get all the drivers that Reactos supports and that is what we're missing. With a 64bit version of Reactos, it should be possible to get a full 4GB address space per process (2GB for badly written ones).
Still the problem of needing people with the motivation, time/resources and skill to do it.
The big problem is that OS/2 is now so old that a lot of people have grown up thinking that the Windows desktop is the ultimate and it is so ingrained in them that there is so little interest in anything else. Saw it the other day when on Slashdot where someone was dreaming of combining the best parts of all the operating systems. He actually listed the WPS as one of the components in his OS, but there was endless comments by people who basically wanted the Win7 interface.