I also immediately thought of Reaction Engines when I saw that EADS announcement.
I have the feeling that the proposed design with 3 propulsion sources is a `conservative` design, but that they would consider Reaction`s engine if it works and is mature. Carrying redundant propulsion like that has got to carry a performance hit (at first I thought they could eject the turbo-fans to autonomously land via UAV shell, but then realized powered flight is de facto necessary for landing sequence if they want a `civil product` and not a Space Shuttle), and rockets kicking in to get to Mach speed (`ONLY 1.5G accelartion` or something) doesn`t seem quite the standard airliner experince (I believe Reaction can provide more continual acceleration). Reaction seem to be progressing quite nicely, and I suspect will find their way into anything EADS does like this. I actually found the 2050 number to be quite late… At the rate Reaction is progressing, something more like 2040 (almost 30 years from now, after all!) seems quite do-able, and the featured propulsion in ZEHST is less challenging technically than Reaction`s approach.

Also interesting to see British companies (Hypermach + SonicBlue) trying the SSBJ thing, in the Mach 3 range. In all honesty, it seems like a partnership with somebody like Dassault (or another OEM) would be most auspicious, if just for marketing and world-wide support. Interesting to see the engine side of things being tackled, which is what`s really needed for such a project.