The thing with chest rig is, don't put anything below your breastbone / on the belly.
The space on your chest and to lesser degree on your sides is kind of "free" in most positions (like people carrying their binos under the armpit). Also very slim backpack pocket (think hydration bladder) or "poacher's pocket" in the back is kind of tolerable even in vehicle or other seated positions. These would be reserved for things you don't need to access fast, like gralloch kit.
My main concern with chest rig would be that it's (usually) strapped on top of your clothing. So it could block using jacket pockets etc. -> doesn't work with all kind of clothing and might require changes how you carry other gear. So you must think it through, chest rig is not as much an "add-on" as a say, rucksack is. You also want to wear it quite snug, and that might present challenges with ventilation and so on.
Good thing is chest rigs come in all shapes and sizes, including "empty" ones you can build any way you want. Haven't seen really good separate pouches for binos, so if you want them on your chest I guess best way would be build up from bino harness. And with minimal chest rig you could always wear it beneath your outer layer, keep the top of jacket open for access and close it when "slithering" (not that I think it's the chosen way of movement for all but the bravest / most desperate...)