The problem with moving away from collectives is that, historically, farms are where collectives both originated, and make most sense. Even in the modern day, farms are by and large owned by giant agricultural firms that simply hire people to manage the land, growing what they are told to grow, using a shared pool of tools.
Of course, the reasons for that are not modeled in DF...
As for nutrition... I'm wondering how that would work, aside from simply demanding a greater variety than two crops, as we currently have. Currently, food is handled thusly: There is a hunger meter that starts at 0, and incriments up to 65535, making a dwarf "hungry" somewhere around 50,000. Food drops that all the way back down to 0.
We'd need to start by having nutritional values for various vitamins for every dwarf, and then raw-ifying what every possible kind of food (including meat) would give as a nutritional bonus... And we'd need to have some sort of model for why you would want to care (such as becoming more vulnerable to disease or injury)...
All that sounds terribly complicated for something that you can't even directly control... I can almost see someone yelling at their dwarves for eating the same tallow biscuits three times in a row when they haven't been eating their vegetables, which would lead to them becoming obese...
Maybe instead of nutrition requirement, dwarf always tries to eat different type of food, and if not available, gets progressive bad thoughts.
For example, a dwarf can remember the last couple of meal it eats, and always prioritize search for one not on said list, and tries to avoid the latest addition to said list. Then, if it always have to eat something recent on said list, it gets bad thoughts like...
"He is getting tired of eating the same thing every day."
"He is angry at the lack of variation in food today."
