The problem is what do you do if someone misses weight on the way to the octagon? scrap the fight?
Then people will say "okay do it a few hours before", which will cause fighters to still try to cut weight.
Ah but I thought of that one too
IMO you could give greater leeway with these weigh ins with purse-penalties to discourage making the leeways habit.
So for example right now they have a 1 lb leeway at the weigh-ins so a LW fighter can still fight at 156lbs. In the new system, allow say up to 5 lbs, with 2 lbs over being a 10% purse penalty, 3 lbs over being a 20% purse penalty and so on. If they're REALLY stupid and can't keep off the McDonalds long enough to even be within 5 lbs of the limit, scrap the fight or do a catchweight like they do now.
Even if a fighter actually takes the financial hit and comes in 5 lbs over, it's still much less weight disparity than we have on a regular basis now with HWs like Anthony Johnson fighting at WW, and not really unfair.
IMO this system would encourage making weight and actually make it easier because there's less temptation to eat a bit more or pack on some extra muscle and "steam off the difference" at the last minute. You weigh what you weigh, it says so on the scale, no steam guesswork involved. You can't even stay within 5 lbs, you face the music for forcing a scrap or a last minute catchweight.