ORAC, thanks for this.
The nuclear F-35 requirement is interesting: it supposedly will cost $400m and the USAF isn't supposedly interested in paying for it.
However, the real question is what impact this has on the NATO allies who operate B-61s under dual-key (e.g., Germany, Netherlands, Italy) as part of NATO nuclear burden sharing. It isn't obvious that any of these states actually want B-61s (modernised or not), or what the actual military rationale for these weapons is.
However, IIRC, the political rationale is that Poland and the "new NATO" members are keen to have tactical nukes in Europe to deter the Russians. But, under the understanding with Moscow when the new members joined, there was an agreement / tacit understanding that no nuclear weapons would be deployed to the new NATO states, leaving the existing B-61 operators to continue to burden share.
What does this mean? Well, if the 200-odd B-61s are still politically valuable to the Alliance (and the Obama Administration seems less than convinced) then the burden sharers will need some nuclear capable aircraft post F-16/Tornado - meaning F-35s and Typhoon, presumably.
For the UK, this would also open the road to a freefall capability instead of SSBNs and massive costs savings to be re-rolled within the procurement budget. Won't happen, of course.
S41