What would you interface to? I thought the idea of DCPU is that it runs the "ship" in 0x10c.
Why not learn real assembly on a living microprocessor and hook it up to real things? There are some instruction sets, like 6809/68000 or 8051, that are very easy to learn and are a good stepping stone to larger architectures.
I'm a big 6809 fan, and you can synthesize a whole '09 system from opencores.org: http://opencores.org/project,system09