I don't know--it dovetails with history pretty effectively. For instance, obsolete technology would almost certainly be sold to minor nations by defense contractors and even by national governments, since they formed an economic good just like anything else--often times, industrial improvements would spread very rapidly, as companies sold processes to businesses in other parts of the world. The only real prohibition on this should be the prevention of trading while at war with the country in question. Otherwise, it would economically have been impossible to stop the flow of ideas, particularly once the technology had become obsolete in its home country. In a more practical gameplay sense, it would help keep minor powers from becoming farther behind than they actually were during the war, and most importantly would simulate the constant technological exchange between the UK and USA before and during the war. As long as things are limited to the obsolete techs, before war and then expanded to all techs during war, it would absolutely be worth it.
