Solution to ... what? I work in this area - I don’t think a “monorepo” is going to solve the numerous difficult problems the US has with modern multi-domain ISR. How do you represent and compare different capabilities from different domains? How do you pick which assets to buy? How do you pick which theatre to deliver them to? How do you plan tactical deployment of your assets? How do you dynamically retask assets in the event of disruption by the enemy? How do you fuse the numerous different data formats to interpret the multi-modal data you receive from your ISR assets? How do you retrain users to use the new capabilities? How do you maintain the assets for a long period of time without cost overruns? How do you get the systems to interface with legacy systems? How do you deal with all the intra-military political issues? These are just a few issues faced by the DoD in the ISR space.
I think there’s a bit of Chesterton’s fence in general around the DoD - the military (and the government in general) has many inefficient, slow, and expensive practices, but while it sounds like a good idea on the surface to tear it up and start from scratch, people underestimate the difficulty and danger of hastily changing or defunding things without understanding why they were put in place.