Uhhh...Britain, through EADS, has partial ownership of the EJ200. Technologically speaking the EJ200 is definitely more advanced than the WS-10X, and at least from what we know so far it may even be a bit more advanced than the WS-15
Not that I disagree with your premise, but you're confusing a few things here.
Britain's stake in the Eurofighter consortium is via BAE, not EADS - EADS is the French-German-Spanish parent company of commercial aircraft maker Airbus which recently rebranded as... er, Airbus*. That's the airframe side though, the EJ200 engine is the responsibility of another joint-venture named EuroJet in which RR is the British contributor (they practically provided the template with their XG40 demonstrator).
There are $40 RC toy "turbofan" engines with TWR in the teens. By your logic, you could upscale that and end up with a 200kN engine with TWR in the teens.
A scale across so many orders of magnitude faces a number issues, most importantly the centrifugal compressors typical of such small engines would have prohibitive weight and drag (external diameter!) when scaled up. Also, you'd end up with an terrible fuel guzzler, as OPR and turbine inlet temperature are very low.
And that's before we get into aerodynamic issues due to Reynolds number (SNECMA's Silvercrest biz jet engine may currently be running afoul of something like this).
Long story short, scaling by a factor of two is a whole different ball game than scaling by a factor of 10000!
Anyway, those are my thoughts; is there any evidence of this happening? Has anyone scaled an engine up before without material/technological advancements?
Not really with entire engines (it's rare that two aircraft of radically different size have the exact same engine cycle parameter requirements, and if they do it often makes more sense to simply use a higher/lower number of the same basic design), but with individual components it's a very common approach. RR built the Trent 500 for the second generation A340s essentially by taking the core & LPT from the 777's Trent 800, scaling them down and fitting the fan from the Trent 700 (A330) to create an engine with higher BPR and lower thrust than the 700 at the same diameter (limited by ground clearance on the A330/340 wing).
GE has been milking the basic design of the 10-stage, 23:1 PR HPC for the original GE90 for all it's worth since the mid-1990s, first removing a stage from the exit end to increase through put for the more powerful second generation 777 engine (PR reduced to 19, engine OPR was recovered by adding a fourth stage to the new fan/booster system). Then they scaled it down for the GP7200 (A380), followed by a more aggressive scale of the original 10-stage version for the GENx on the 787, to which they've now added a stage to make the GE9X for the 777X!
In fact, I would not be surprised if the 10-stage, 22:1 PR LEAP-1 HPC owes a lot to the same basic design, with performance relaxed a bit to take into account narrowbody engines accumulating cycles (as opposed to hours in cruise) at a higher rate.
I'll believe it when they do it.
RR (well, still Bristol-Siddeley at the time, actually) Olympus in the mid-1960s, with thrust levels of 130 - 150kN.
It was baselined for a number of UK combat aircraft designs - all of these projects were eventually cancelled but the 137kN Mk.320 flew a couple of times in the TSR.2, the 150kN derivative (BS.100 for the VSTOL P.1154) at least made the test bench and of course, it eventually became the 170kN Concorde engine.
* You read that right, the Typhoon is now officially an Airbus! Somehow doesn't quite work in the same way as the Superjet being a Sukhoi, or a Falcon biz jet being a Dassault though
