Great idea Richard! I like the mentioned above... i would add few more
-Do you use different diabolos for different tricks? I mean do you change for vertax, 1 diabolo, 3, 4....? And the sticks? And the string and the string lenght?
-How do you keep in mind all your tricks and in order to do not forget them? Do you record yourselve or write down the tricks?
-Do you find the Siteswap useful? Do you think it should or it could be improved?
-Bearings yes or no? Why?
-Unfortunately diabolo is not very popular in many countries, any ideas how to make it more visible and popular for all around the world?
-Do you like competitions (EJC Diabolo Battle, Redbull PAO, FDC, etc...)?
-How are your juggling skills with other props (balls, clubs....)?
-Do you go to juggling conventions? Why the diabolo players are always in a corner separated of the rest of jugglers?

Cant wait to see-read them!!
I will add maybe more later