To me, adding on the possibility that it could be some sort of Mach 5 super airliner, suggests that the practicalities of it as an SSTO platform are perhaps not

To me, adding on the possibility that it could be some sort of Mach 5 super airliner, suggests that the practicalities of it as an SSTO platform are perhaps not nearly so compelling as once thought Ding! Yeah, that was my reaction. If SpaceX get the reusable first stage tech running on Falcon 9, then they shave $40M off the cost of each launch (the first stage fuel and oxidant costs $300,000; the stage itself, including nine motors, costs around $40M). Even if each flight costs a couple of mill to refurbish and can only fly 10 times, they'll still have cut the $40M price to around $6-7M. Meanwhile, here's Skylon, a decade late off the starting blocks. With the Sabre engine running on liquid hydrogen, which is a beast to handle, with valuable He as a consumable. Frankly, the airliner option looks silly to me. The only real target market for a Mach 5 in-air vehicle is the military.