It is very simple;
If the continental championship will be held first: Most likely USA, BRA, CHN, SRB and Kenya will qualify. Other top European teams such as ITA, NED and TUR will get top 3 position in World Cup (or whatever FIVB wants to call it). 3 other positions can go to other CEV teams such as RUS, AZE, POL (GER or BEL or even BUL with their full roster). With this order, there can be 7 strong European teams in OG. However, if World Cup is held before continental tournaments, CHN, USA and BRA will get the 3 spot (SRB might grab BRA's slot indeed). Then, THA, DOM and ARG will win their continental tournaments. This means only 3 spots will be left. Even these 3 will be taken by european teams there will be only 4 CEV teams in total. Thus, the order of the tournament will make a big difference in the composition of qualified teams
Forget about such changes first tournament (World Cup or other name) will be the first one as FIVB needs motivated teams and strong competition.
There might be (I guess) only possible change between 3 world FIVB tournaments and continental qualifications.