It's possible, and has been discussed previously. So far as I know, no one is working on such a project though.
Most likely, if a Symbian port ever does happen, it will be after that OS becomes fully open source. However, by that point, the next Maemo device will be out, the N800 and N810 will be growing old, and therefore, interest in developing such a port is likely to be small and dwindling.
So you guys think.... nokia is already running symbian on the NIT's just to test the viability?
At this point, I suspect Nokia's more interested in "testing the viability" of moving from Symbian to Maemo than the other way around. However, I do imagine at least one person within Nokia has put Symbian on a tablet at some point, if only because all the bits were sitting right there and it was Friday afternoon...
