Agreed. It would still necessitate the closure of LHR of course, which remains the elephant in the room when discussing anything other than an extension of LHR (in whatever guise that expansion comes) but certainly interesting nonetheless.
The LTN proposal may be compromised by the fact that the local councils own a large proportion of the airport I believe, so could get just as political as LHR but in a different way...but it wouldnt be fun without a political bun fight!