i think it's very unlikely refueling will return at any point for races of 2 hours or less. it adds cost, risk, and enables the cars to go faster (1. lighter fuel load, 2. smaller tank, 3. less dynamic range between full and empty). regulating bodies like FIA desperately fight for the opposite of those things every year.
the f1 field has never been closer, yet things overall are pretty stagnant. most overtaking occurs because of drastically different tire conditions, followed by drs. the problems are (imo) :
track design does not lend itself to passing. there is only 1 line to take, and if you're not on it you're screwed. this addressed in a couple new tracks (india, austin) with big corners that allow for multiple lines (huge entry, narrow exit). abu dhabi in particular has it backwards.
aero is king, and when a car gets behind another his aero shuts off. the only answer i have is to further limit the downforce produced in the first place.
the same (deliberately) rapidly-degrading tires that can produce passing can prevent it. not only is it necessary to protect tires at all times, but the amount of marbles off line is simply amazing. drive on that stuff and you are done.
qualifying. if you spend all day sorting the pack from fastest to slowest, don't be surprised when they finish the race in roughly the same order.