I think the rights reverted back to the author.

I'd love for Temeraire to be a series, in my head I had Tom Hiddleston as Laurence but he might be aging out as well. Though Richard Armitage would also have been awesome.

All I can think is that it would cost a boatload of money. Boats, war and dragons.

I'd watch it as an animated series, then it wouldn't matter how old Armitage or Hiddleston were.