Even last gen titles like DA:I and GTA V are much too CPU intensive to port to the Switch.

This actually isn't true, though. The CPU on the Switch may not match the clock speed, but neither do the PS4 and Xbox One; the advances in the CPU's actual specifications otherwise make them come out on top. The K1 was claimed to be stronger than PS3/Xbox 360 CPUs, and the X1 is much stronger than that, even underclocked to 66%

As for an x86 SoC, it's not a smart idea, ARM was designed for a reason. There have been attempts to make x86 SoCs and they either ran much worse than ARM chips at similar power levels, or required much more power to run better. ARM excels at efficiency per watt and x86 doesn't, that's just how it is. With computers and laptops this isn't so much of an issue, due to being plugged in all the time for the former and the gigantic batteries used for the latter. With tablets and handheld devices, however, it starts to get worse. You act like Nintendo could just easily invest in an x86 SoC; has it not occured to you that Intel and AMD have been working on making them for ages? Currently Intel's x86 SoCs are used for the Surface Pro, and while it works decently, it is still FAR worse at performance per watt than an ARM chip. The reason they decide to go with x86 SoCs for the Surface Pro is so that no porting would have to happen at all. However, this is a moot point when it comes to porting to the Switch; it runs on a different OS, after all, as well as a different graphics pipeline, so every game would have to be ported. Furthermore, porting from x86 to ARM and vice-versa is not as hard as you claim, it is VASTLY easier than porting from the complicated CPUs of the PS2/PS3. As a programmer I have written for both, and unless you're getting into the REALLY low-level stuff (which the average programmer is not doing and will probably not need to do even for porting an engine over), you're not going to have major issues porting from one to the other; in fact, I would say that the different OS and different libraries would add more work than the x86 to ARM switch. Switching from ARM to x86 would be a terrible idea for a handheld, it would do way more harm than good, and it's not something you could just magically 'invest in', as Intel and AMD have been trying for years and haven't even come close. The best solution would be to use a better ARM chip right now, and that's what is most likely going to happen in the future.