"But seriously be practical. Pure math will only allow you to do 1 thing in the future and that is teach math "
Smartest thing I've seen posted on NG in a long ass time. If theoretical mathematics is your bag of crisps, you can easily master things that do not yet have any practical application whatsoever. The sad truth, but don't let it depress you. On the journey there, you may find that you are in possession of a universe of interesting solutions, to problems vexing others. I'll give you a crude example:
Not so long ago, no one knew what backface culling was.