We will need to see a lot more details before we can safely say that this is a viable design. 'Just using a gas-turbine to generate electricity' is fine, but you still need to deal with the inlet design as mentioned and you will still need to generate enough electrical power to sustain supersonic flight after getting there. We're not talking about a small APU-style generator then. Mixed-cycle engines have been proposed before, going back a long way, but have we seen any running? I'm also surprised that they want to aim for Mach 3. History shows that using a conventional structure is easier to produce and operate, and that leaves you at Mach 2 and a bit (127 deg C on the nose was Concorde's hard limit). Can you go faster using composites? We're into relatively unknown territory there as this is not a quick dash to high speed, but sustained flight for several hours at that speed. The only type that has done that before was built using lots of titanium.