I had heard the MAN facility is close to being formally announced. With Theresa the appeaser at the helm, probably makes no difference to the UK stance on pre clearance.
It's also a bit premature to be reviewing the pre clearance facilities. For MAN at least, USPC is a long term fit, with it being 2019/2020 at the earliest before its up and running. Trump has 4 years, 8 at most, at the helm, so, this immigration thing is not a long term issue.