More topic suggestions:
Heya culture/differences. Why are some small, some big, some collegiate, some still middle school recruits. The whys of these things, in particular. Izutsu is of particular interest just because it seems odd for reasons that aren't widely known.
Recruitment in general: how it's done, why rikishi choose particular heya or how much some need to get talked into it. Are rikishi seeking heya or the other way around?
Amasumo: corporate teams, the 'big' high schools, universities. What's the life of a corporate amasumo guy like? How does high school choice work in Japan, and how do the big schools get the good atheletes? What incentives are offered at the university level? What happens to the university guys that don't make it: do they get a good enough education to get a proper job?