First, I'll assume your referring to ONLINE ratings as opposed to LIVE. That said, those ratings are about 300+ points inflated at most levels in my estimation. So, we're now talking about someone improving from about 1400 ELO to about 2300 ELO in a single year.
My opinion (if the 1400 ELO represented true initial skill): extremely unlikely, but not impossible. Just my view, for what it's worth.
Given that everyone comes in at 1200 regardless of actually playing strength, any strong player's rating will exhibit a rapid increase, however.
O.K, so I have been a member of chess.com for well over a year and I have reached the magic level of 2000+. This was done through hard work on openings and some tractics training, as well as developing some positional grasp.
However, I have seen people improve from around 1700 to 2300 and even 2600 within the same period of time. It is supposed to get harder the higher you climb, so what is the secret? Can some of these elite players share with us?