Functional exercising in the off season and during the season will definitely get you in better shape. That is doing exercises that apply to skiing eg squats, single leg jump and catch, plyometric jumps over boxes etc. Core training, balance plates all will help.
The biggest physiological limitation is our brain! This processes all the info and makes it happen. This should open a minefield :-) if you don't possess the mental capacity, then you will be limited. Its your brain that causes you to rotate and have lack of separation. Here's why - you have hardwired into it the fear of falling from years of experience, that the automatic muscle response is to turn into the hill. This is the neutral pattern. We then have to break this pattern and rewire it. During this process our brain does lots of comparisons, is this right? We add fear, uncertainty, preconceptions,history amongst other things at the same time trying to create this new pattern or sensation. It'll feel strange and require conscious thought and intention, as soon as this is taken away eg with fear or distraction we revert to what we know, the default. I suspect this is what hinders most people's progress. They don't know what the new pattern should feel like, they lose attention and intention and revert back to what they know and keep doing this way therefore reinforcing their previous patterns which is no longer useful.
Let's face it we all probably free ski lots without conscious intention, because its become an unconscious pattern, so we make the current neutral (in some case faulty)patterns stronger.
Without babbling on for to much longer, the key to improving is skiing with a focus and intention all the time. Get external feedback from mentors and video footage so you can build up your own internal feedback system. Manage your own brain, control your fear, change your beliefs (note beliefs are not truths or real!),be open to change and new sensations. Be willing to be on the edge of your comfort zone because if it's comfortable then nothing is new.
Our biggest physiological limitation is our brain. Train it then your skiing will get better. Just my thoughts.