SSSETOWTF has it right. If you're going to go up against, effectively, a 'superpower' (China/Russia/USA) that can afford an integrated multiple-battalion SA-20 ADS, then B2/F35/F22 is what you want.
But the lesson that still hasn't been hammered home since the fall of the wall is that our demonstrated need in the last 2 decades has NOT been for this level of capability. Yes, we'd all love to have it, but not at the expense of ridiculously low numbers of platforms.
Complete WAG here, but what are we likely to pay and what are we likely to get? Say £6Bn in procurement & development costs to receive a fleet of 60-70? Say 10-15 FE@R? Effectively no more than 3 deployable sqns? And while I take the point about economic benefit, such an arrangement could be constructed for ANY future procurement, thus the question of underlying cost is relevant, particularly within a constrained Defence funding envelope.
Aston Martins are wonderful cars - but sometimes all you need is a Ford Transit.