There is no rewards at the end of the season so far. At other hand, higher leagues bonus becomes significant after approx 2400 medals 70/70ks and higher, so it boost your income significantly.
Don't really want your TC, other than the necessity of not losing 149 medals and it sometimes yields a diamond or two.
We'll see when I've climbed another 1100 medals and you appear on my "Next" button, but there again with this game's match-making it could be tomorrow. Or the day after would be more suitable when my Academy is upgraded and I have a couple of sabotages available.