It'll be interesting to see what happens when Character Options/Underground Toys switches to the 3.75-inch scale. Some classic Doctor Who figures were never released in the 5-inch scale...
Of course, plans can change, but for the moment, UnderGround Toys and/or Forbidden Planet can still "commission" figures in the 1/13 scale. That's been the business model that has resulted in the bulk of the "classic era" figures after that initial wave that included the 4th, 5th and 6th Doctors along with an assorted collection of monsters. Those were for general distribution and execxuted by Character Options itself. But since then, UT and FP have shelled out "X" amount of money to Character up front to have a particular character made.
Character Options will focus strictly upon the current program and what figures evcentually offered will be in the 1/18 "Star Wars" scale. I know what you're gonna' say, that we won't get the Doctor in his new longer purple coat or Clara as 5.5 inch tall figurines. Actually, Alister Dewer has hinted that if UnderGround Toys and/or Forbidden Planet CAN commission long coat Smith, Clara, or say, a "Spoon Head" robot in 1/13 scale if they are willing to shell out the money before hand.
It's just that the widely distributed figures one can find in the "high street" stores (department stores and those located in malls to us Americans) will be the smaller scale focusing upon the newest episodes.
Sincerely,
Bill