My experience with color neutrality (for what it's worth):
I swapped to full CN probably about a year after I started cubing. I think because I did it so early it was easier for me. It probably took two weeks or so to get comfortable. This was a long time ago (5-6 years), so my memory is a bit vague, but if I am remembering correctly, at first White/Yellow was easiest, then Red/Orange/Green/Blue became easier than White/Yellow for some reason, then finally they all became equally easy. Now, there is legitimately no advantage/disadvantage for any color for me. At one point in my career, it would have been hard for me to tell you what color I solved on. I think at my speed (10-11 global, trending towards 11 these days, lol), full CN is really good on 9/10 scrambles. The tenth is a doozy, though. These are the scrambles where you can't find an easy cross on any color, so I tend to waste some time deciding what color to start on. This is getting very rambly, but one point I want to make is that I think if people would commit to full CN, then probably within a year (#arbitrary number), it would be like you have been full CN all your life. As some people have mentioned, dual CN may be better at a high level, so as not to be messed up by that tenth scramble. That seems plausible to me.