The schedule is pretty flexible, as this is a long term fleet renewal oriented development.
So I think taking time up from to make the right decisions is very appropriate. Costs are largely determined by these early choices, so this is the best chance for getting it right.
These rationalizations aside, it is also a reality that Boeing has been late and over budget on almost all its developments, both civil as well as military, throughout this century. So it would be surprising if this project, which is projected to scale a concept from a 6,000 pound vehicle to something in the 30,000 pound class, were not to experience substantial slippage and cost growth.