Kerbal Space Program

The Engine Plates added in Making History are amazing -- they fill a large need (see all the hacks people have done to cluster upper stage engines in the past) in an elegant way without really increasing the part count on your ship due to the included decoupler.

Seeing as they don't really have anything specifically to do with historic spaceflight, it seems like they could be moved to the base game to great benefit:

• Enable wider sharing of crafts built with them
• Reduce need for similar parts in mods
• Encourage mods to build new functionality on top of them without worrying about limiting their audience