That's just how the BBC does things, pretty much. In the vast majority of cases they only work on a season by season basis, as far as both contracts and commissions go, so I wouldn't read too much into that.
Capaldi is a bigger fan of Who than even Tennant was, and this is his dream job and role, so unless something goes seriously pear shaped I don't think he'll be in a rush to move on any time soon. But as he likely won't be on our screens until next august or so, according to the rumours, that gives Big Chief plenty of time to get something sorted before the show is off screens next year.
We'll see the outfit sometime soon (and I imagine licensing will get official images as soon as they are available and the choice has been made), so at a guess I'd say that Big Chief will probably start working on him during early next year, with hopes to put up a pre-order some time during the next season. They may have started on the head sculpt already for all we know. As the current Doctor I'd imagine they will want to get him out as soon as practical, no matter what, though.
Honestly, if I were to guess I'd say that after the Hartnell pre-order we'll see one more release next year (Eccleston or Hurt perhaps?), and then Capaldi to round the year off. That way they should be able to deliver two Doctors next year (Hartnell and whoever), and have a pre-order for a third (Capaldi) done and dusted by this time next year (with a bit of luck).
Still, just have to wait and see, I guess.