John's put a lot more thought into it than I have and he's run at least two sessions with playbooks tweaked for modern warfare. The feedback he gave me was all very positive. The two of us have discussed the Regiment's span of history and we think it can probably cover WWI to the near future with "minimal" modification. Purists will want to, at the very least, edit the weapon tables both under elements of warfare and on the playbooks themselves. If you're into hacking, you can try something further afield.
Most modern gadgetry probably falls under Assess the Situation (modern tech gives you new and better opportunities to ask what's going on) and Fire Support, the Officer Move (which allows you to call for fires). Petition up the Chain of Command and the Soldier's move Heavy Weapon can also be used to get your hands on the fun toys!
There's been a little discussion here too:http://apocalypse-world.com/forums/index.php?topic=2629.0