It does sound fascinating, granted, but it doesn't really increase your employability does it? You said that you can still do Investment Banking and Law but what benefit would you really get as an Investment Banker with a Philo degree instead of just an Investment Banker (plus the added costs)
I love History, and continue my interest in studying history despite doing a STEM degree, however while Philosophy is interesting, but I disagree with you about employability. What do you do as a straight Philosophy graduate?