There is little reason that a $200 dock couldn't match Scorpio, considering this last holiday you could buy a $200 GPU from Nvidia with 6GB VRAM and match the 6TFLOPs RX 480 (and exceed it in many games)
The dock alone is going to cost you maybe $15 dollars to manufacture, leaving plenty of room for a 4+ tflop GPU in the dock for retail $199. They could market it as a 4k dock and heck they only really need 4GB VRAM in the dock rather than the 6GB, so they could probably even undercut that price point, and that is just this year, next year they might be able to do it for $99, it's hard to say really, but the idea behind SCD makes a good amount of sense for Nintendo to pursue if they want to pass hi fidelity graphics cost onto the customers, could even add 4K DLC packs to games just for texture packs.
Again given what we know, there should be plenty of overhead in Switch for higher clocks too, I'm not technically aware of a reason that the A57 cores couldn't hit 1.5ghz even portable other than battery life, I mean another ~watt of power draw isn't going to mean much, and that should put it in line with about 6 jaguar cores at 1.6ghz like PS4.
We also have iterations to think about, a "NEW" Switch could be over twice as powerful in the same power envelope and even match PS4 if they wanted to, people tend to think that power envelopes make it impossible, but 4SM @1.25ghz on 16nm pascal with 4 A72 cores @ 1.7ghz (same power draw as 4 A57 cores @1ghz 20nm btw) would draw less than 20watts and that should be fine for the docked device, which with the same performance ratio gives you 512gflops portable. (this is just speculation on a future iteration, while the technology was available to do this last year, no one should have expected this and it was always a best case scenario, but for an iteration, it makes a lot of sense, as it would handle the rumored Switch specs docked performance on the go)
The true innovation here though is how modular the design really is, I mean Nintendo can have you plug the switch into any new gimmick they want. VR? check! some stand alone new device powered by switch? check! overclocking the switch adds plenty of performance as well, because even the version of the switch we've been talking about for the last few pages is capable of CPU performance on par with PS4 pro (if upclocked) and GPU could match up to half of XB1 if upclocked when docked.
They can use switch as a trojan for pretty much any new idea they want to push since it really is just a stand alone screen with capable cpu performance and a modern GPU that ensures compatibility with the industry's gaming pipeline.