Polonius hopefully arrives next year and reduces the burden here further. Partial field borrows would be huge so that something like obj.set_bar(obj.foo()) would work.

Given the troubles with shipping Polonius, I imagine that there isn't much more room for improvements in "pure borrow checking" after Polonius, though more precise ways to borrow should improve ergonomics a lot more. You mentioned borrowing just the field; I think self-referential borrows are another.