[Slick]

I think the idea has some merit. Rather than a strict "either, or" maybe it should increase the cost of "switching over". Keep in mind that the timescale of a game is one extended war, so empires are in war production mode and leadership needs to provide clear direction without constantly shifting priorities around. If research priorities are shifted around, there should be a penalty.

Example: Shields or armor.
If you choose armor, then the cost of shield research increases due to having to switch over your economy, technology, ships and equipment. You still can research both, but at a much higher cost than either one individually. This would allow you to research one branch much farther in the same time if it were done exclusively.

This kind of research model would diminish the ability to quickly respond to what the enemy is doing and provide a counter. As such, it would need to be done carefully, because this aspect of SE4 is one of the things that makes it a great game and a poor implementaton might ruin the game.

Slick.