Im still curious about solving structural heating issues. The hypersonic tests carried out by the USA have used the fuel as a surface coolant. If this fuel is now used for cooling the airflow, not sure how this will be dealt with. The RCC panels developed for
shuttle were horrendously difficult and expensive to produce (it took some convincing to spare one for destructive testing as part of the Colombia accident investigation as they were in extremely short supply). The vehicle will be exposed to extended periods sonic shock compressive heating, Be interesting to see if manufacturing has made RCC or similar technology more commercially viable.
I think the original design with the engines on the wing tips will be a no-go; the unstarts suffered by SR71 resulted in a few catastrophic losses. I can’t imagine that this additional level of yaw with next to no aerodynamic damping and limited RCS output would mean any form of asymmetry would be recoverable. That lends itself to something like a lightning engine configuration or some form of very rapid thrust control on any symmetric engine.