The UK is not in any position to reject out of hand such a proposal as it already operates a similar pre clearance in France for those using the tunnel. Indeed the officers were at one point inspecting Belgium nationals illegally on trains when they were not going to the Uk.
Pre clearance has many benefits for the passenger but the practicalities of operating such a system are huge but may be surmountable with significant investment.
The issues today are many ranging from US suspicion of everyone entering the country who is not a US national, to broken systems and insufficient resources being made available at US entry points.
There is an arrogance that says people will travel regardless of inconvenience but whilst that may be true of business travel I think it is now a big consideration for leisure travel. 10 hours or more to cross an ocean is a well an good, but if you then have to stand in line for 2 or 3 hours and be treated badly whilst doing so, is not the welcome many want.
I recently entered via DFW and what a pleasant surprise it was. Automated systems ( which did not work ) and well manned and reasonable numbers immigration staff. Meanwhile JFK is simply vile and LAX horrific.
Mind you, arriving at LHR as a UK/EU natioNal can be pretty unpleasant. What is must be like for real foreigners I can't begin to imagine.
But it does not have to be so, Singapore leads the way with immaculate, well mannered and thoroughly pleasant and welcoming officers. Yet they still can post death to drug traffickers on the bottom of the landing card!
The answer therefore is pre clearance but not boots on the ground pre clearance. Use systems and effective IT to profile passengers in advance of travel. My family on a two week trip to Disney land with an 80 year granny is not a threat but we are treated as one and that needs to stop. Take my finger prints if you must, my picture also but please do so efficiently, pleasantly in a welcoming manner. I am even happy for you to keep it if it will help me enter again in 12 months time!