I just read the new Space Marines codex, made for the 5th edition rules. It introduces (or re-introduces) some units that were mentioned in previous editions, and organized them in ways that would, interestingly, make for some pretty good ideas for any expansions that DoW II would have.

Of particular note are the newly reorganized veteran units (the ones without Terminator armor) and the Master of the Forge, which would make for a good upgrade to the Techmarine, if there is some odd new power that would somehow upgrade the Techmarine to a Forge Master.