BA already has far too many slots at LHR, so I'm not sure how the EU Commission - which would almost definitely be brought in to oversee the process - would react to that.
Does anyone know how many extra slots this would yield per hour? I heard a figure of about 6%.
There is currently a government consultation process into regional flights and I'm sure that many of the responses will focus on access to Heathrow, from places like JER, IOM and others. For example, is it a good use of valuable slots at LHR for the likes of MAN to have around 17 flights a day - with A319s and 320s - when other regional destinations lose out; couldn't MAN have an express rail link, for example?
As for the US, that will depend on the provisions of the bilateral, when it's finally revised. Don't hold your breath, though. The UK carriers have the DFTR wrapped around their little finger, asking for something that won't ever be granted (cabotage), purely to delay the process, which will bring more competition to LHR.