I'm assuming there are two reasons for implying people shouldn't change.
if you're never done graphics programming, Vulkan is not the API for you. Khronos and Microsoft are recommending that simple projects or novice programmers stick to OpenGL/D3D11 rather than trying to jump to Vulkan/D3D12.
Where did you get this from? Link?
While Vulkan like DX12 or Metal will require more code, I don't think this makes it more complicated. In fact I rather expect Valve to ship examples with MIT licenced code. So I guess around August/September you could start programming for Vulkan. I'm curious if X-Plane etc. will make that move.
SDL is cross platform but I've only used 1.2 for texture and sound loading. OSX install was a bit annoying. Lots of wrong osx examples floating around...
1. Completely revamped architecture: this one should be obvious, particularly for people that may not have much experience with graphics a lot of the changes to how things work in relationship to the actual work being performed on the cards may be confusing. Also a big one would be a lack of material available, you'll be stuck with pretty much whatever documentation you get with it.
2. The whole design they put forward with on Vulkan is that they're removing the waste and the safety limits on the code, the new style is supposed to be similar to C++ in nature, allows you to shoot yourself in the foot very easily if you don't know what you're doing, and you may not even realize you're doing it.
I don't think people will listen to such advice though, and honestly I can't really blame them. Someone out there has to try out the new thing and screw up till they start to understand it. If anything the advice is that you'd be much more productive with the tried and tested API's.