Last week YouTube released 8K videos option to view.
But I don't have a Macbook yet and I was wondering if anyone here test it.
and comparing to the basic 13 and the basic 15 inch retina
No it won't.
Because whether or not the CPU will be fast enough (it probably is, but anyway...), your display is nowhere near high resolution enough (it will look no different to 4k), and the GPU does not support 8k resolution - and neither does currently shipping HDMI, Displayport, DVI, etc. i.e., even if your CPU can decode it, and your GPU can output it, no cable is available to attach to your Mac to output it to a display.
There's zero point trying to run it on a 13" display anyway - 4k is already well beyond what your eye can see on 13" anyway. 8K is only really useful if you're dealing with home cinema size displays or larger.