It will be interesting to see if he can truly do both. Weight is such a speed penalty for sprinters, yet such a necessity for football players. Realistically, wide receiver is probably the only position that he can play and try to maintain that track/football weight balance.
From a long term financial point of view, professional football may be the most lucrative choice. A quick search on Usain Bolt's net worth comes back around $90 million and arguably he is the GOAT for track and field, at least for sprinters. Top defensive ends in the NFL are making $25 million/year, wide receivers $30 million/year and tight ends are making $17 million/year.