Surprise news arrived this morning from the promoter for Yes's Japanese dates in April. The announcement is only available in Japanese, but says that, due to prolonged medical treatment, Jon Davison will be taking the lead vocal role in Yes for the band's April tour leg instead of Benoît David. An extension of that tour beyond Japan is also announced, with the band to play Jakarta, Indonesia, and then a final show in Hawaii at the end of the month. This will be the band's first visit to Indonesia and, indeed, I believe only the second time they've played an Asian show outside Japan (Singapore in 2003 being the other time).
I'm sure more details will emerge over time, but my tentative understanding at this time is that the band had been planning to tour with David, but a problem emerged very recently (late January, at a guess) and Davison was brought in quickly to allow the April tour dates to go ahead. This seems to have been a change forced upon Yes rather than one they wanted to take.
I have no further details on David's medical problems, but wish him a prompt recovery. The obvious question is what happens after April. I don't know. It seems quite possible that, right now, the band don't know either. The Japanese promoter's announcement isn't clear... at least not after it's been through Google Translate... although one might read into it an implication that Davison is merely filling in for this tour leg, implying David will be back later in the year. The band have been looking at summer dates in Europe and North America, although nothing has been announced yet. What happens with those plans is also unknown.
For those of you who don't know him, Jon Davison was born in California and was a childhood friend and bandmate of Taylor Hawkins, now drummer in the Foo Fighters. Davison moved to Seattle and played bass in psychedelic band Sky Cries Mary. He later joined Yes tribute band Roundabout on vocals. He more recently joined Glass Hammer around 2010, appearing on their two most recent albums, If and Cor Cordium.
14:43 edit: The official Yes Facebook account has now confirmed the news with similar text to the earlier Japanese announcement. It describes David as having still not recovered from his illness at the end of the 2011 European leg, which led to three shows being cancelled. The announcement talks of Davison "joining [...] for this leg of the tour", so the implication still seems to be that David should be back in due course.
The surrealism of someone whose name appears to be a cross between Jon Anderson and Benoît David joining the band has not been lost on fans. Jon Anderson has previously guested with Glass Hammer (just before Davison joined), a band many feel are quite Yes-ish, and Davison also performs along side CIRCA:'s Johnny Bruhns in Yes tribute band Roundabout.
22:29 edit: I am amazed at how quickly information emerges these days. It wasn't like this when Wakeman left in 1997, or Sherwood left in 2000. Anyway, I expect there's plenty more to emerge, but what do we currently know... It seems David walked in January, leaving the band uncertain whether they could make dates booked for April. An approach was made to Jon Anderson, who said no, although we don't know what terms he was offered, of course. Very recently, Davison was booked.
David's situation is unclear, but the evidence now appears to be pointing to his being gone permanently. It occurs to me that Yes may be in no rush to confirm whether Davison is staying for the long haul. After all, they may want to see how they get on with Davison before rushing to confirm any permanent status.