NC for this post. I work at a school that's at a very early stage of considering this (not LU). I get quite bored of the constant cynicism on MN and elsewhere about private schools' motives about everything, all the time. The reason we're looking into this has NOTHING to do with being disappointed in our GCSE grades. It has NOTHING to do with wanting to stop our pupils leaving at 16. (A new course would need to be fully accredited, externally moderated, and recognised by universities for us to consider it, so our pupils could still quite happily move at sixth form - just as many international students already do, who haven't done GCSEs). It has everything to do with us not liking the GCSE curriculum very much in many subjects.
I totally get the arguments that say that private schools shouldn't be allowed to do this, because there should be a universal qualification at 16. I also take on the chin the argument that it's a bit arrogant of private schools to think they can write a better curriculum than the rest of the country, and that it's unfair that only those with money can benefit. But I would counter that quite a few state schools are also calling for an end or a change to GCSEs, for similar reasons. And that there are benefits to private schools being outside state control - yes, mainly for their own students and parents, because they can choose the education they want for their children, free of the diktats of government, but also because it allows schools to explore the alternatives, look at what works, have the freedom to try new methods etc, which to some extent can then filter out to the state sector (whether directly, though private/state partnership, or indirectly, through published research papers and resources, or through lobbying of government).
We may or may not go down this route. Other schools may or may not follow. The government may or may not decide to radically reform the age 16 qualifications. But if they do, i imagine they'll be looking quite closely at what schools like LU have done, as well as at courses like MYP. But in the meantime can we not at least have a debate about the merits of change, without just going back to the same old 'private schools are purely self-interested' arguments ALL the time? Some of us are actually pretty interested in pedagogy and teaching and learning approaches and curriculum design in principle, not just because we want to keep the fees rolling in. You know, like state school teachers are.