The androids are being upfront with me that they have never transferred a human mind from a human as badly damaged as Chekov is. As such, they have said that it would be far better if we wait until Bones is fully back on his feet. That way he can keep the body as stable as possible during the procedure, greatly improving the odds of success. Since this is going to be an all or nothing shot, I agree with erring on the side of caution.
Besides, as Mister Scott has so drolly pointed out, odds favor this happening again.
