I think for anyone looking, it's worth considering which airline works best for you. Personally, I prefer Skyteam to Star, and from that point of view, AFKL's Flying Blue is a fair programme in the sense that it's not great for rewards (that part is revenue based) but it's actually pretty good for status. Note that the initial climb is a bit slow as I think you go back to zero with each new status, but once you are at Gold or Platinum, iit's actually fairly easy to maintain. You'd get to use one stop on AF, KL or VS but also ex-DUB on DL.

If preferring *A, I think that many people seem to like TK. A3 used to be very good but has been downgraded a few times especially if you don't use A3 itself that much, so I've effectively let it slip.

Having said all that, I think that there may be value for anyone to wait for a few days. Unlike those wanting to stick to OW, moving to ST or *A opens the prospect of status matches and I wouldn't be surprised to see many of BA competitors launching aggressive status match campaigns in coming weeks, presumably starting with VS on BA's own turf. Frankly, they would be crazy not to.