I'm assuming those that are lauding this pre-clearance news as the holy grail are not regular travelers to the US.
Having once tried this at Dublin, I honestly didn't find it saved me any time - the time you save at the US end is lost at the home end. When compared to the alternatives now increasingly available at the main US entry points its advantages wane:
1. Global Entry is thee way to do it if you are a regular traveler to the US
2. When you are a returning ESTA ie it's not the first time you've used that ESTA, you basically go to an automated booth that actually works, and fast (take note UK Border 'Force') then it's usually a short queue to an officer that completes the process in a jiffy.
Pre-clearance will no doubt help the tourists speed their way to see Mickey and Donald and first time visitors will benefit but I fail to see how this in itself will boost passenger numbers. Get rid of APD, now that would be a game changer.
One specific thing about MAN that might make it difficult is that it has flights to the US from all three terminals - that would surely require 3 separate facilities no?