1. Set internal timers for Preston's quest giving. I love to roleplay that I am helping the Commonwealth by being part of the Minutemen, and I realize that with the post game being what it is, Bethesda might have seen the Minutemen as their one show pony, and so they made the quest rate unquenchable. This is proving to be a horrible idea, because it kills my desire to want to participate in these AND shatters the illusion of the Minutemen, because you have a crisis every time you solve one, and it just feels like an unrealistic tempo, even in a raider filled wasteland. They need to fix that badly, because I also like to bring Preston with me, and when you get on a roll with those quests, you never get a break when he's around.
I would say having a literal 3-6 hour timer would be great, at least for the radiant kidnapping and creature/raider/mutant kill quests. And by that I mean, a kidnapping happens and you have another 3-6 hours before another kidnapping will occur. A raid can happen anytime after, but it will trigger its own cooldown timer.
2. Add more radiant quests, such as:
-property disputes
-murder investigations
-caravan and/or trader escorts when they are traveling to dangerous locations
-medicine/food delivery
-Minutemen training exercises
-and so on
I feel like dialogue is the red-headed step child of this game and it would greatly behoove them to improve upon the non-violence based activities present in the game, of which settlements are a key (if honestly the only) part, so they are a great place to start.
3. Make settlements improve over time. This would be a huge commitment of resources and might be nigh impossible I don't know, but I feel like we can manage our expectations to make it more doable. What I have in mind is basically having the houses and other locations where you set up settlements get repaired over time as your settlers live there under happy conditions (maybe 80% or above). So Croup manner would go from being a bombed out hellhole to a nice home again over time. Same goes for the homes in Sunshine tidings and Sanctuary. Just basic phasing over time that goes by in say 3-4 tiers. For the stuff that we build, it would be great if it had the same kind of phasing. So the wood houses start off looking like crap, but then over time, the material is improved upon. It would be amazing if they could program settlements so that over time, the settlers would place nick nacks and other personal valuables on tables, shelves, etc. So the place would look alive organically. As it stands, making things nice falls solely on our shoulders, which I suspect is the price we pay for the unlimited freedom of customization, but I'd honestly sacrifice that freedom in certain locations if it meant we could see improvements like this. It would make the whole system feel more alive.
4. The ability to lose your place as general if you screw up bad enough. Keep losing settlements to raiders or let your settlers suffer at the hand of Super Mutants and eventually the Minutemen will take a vote of no confidence in you. Dedicating yourself to fixing things up again and you can earn your place back as general (I think in your absence they promote a stand-in general who is barely competent, making your reclamation of the title make sense). I think this should be a post main quest thing, as most players don't really always have time to invest in the settlement stuff and it should come after they have the radiant quest rate nailed down.