Currently the WT teams decide which HC and .1 level races they wish to do. They cannot do .2 level races. There are limits to the number of WT teams allowed in HC races (70%) or .1 races (50%) so the organiser will make the final choice if over subscribed. However, many races will not reach the limits as this would severely over commit WT teams.
The new setup for 2017 seems to be up in the air as there is disagreement between UCI and teams about the new WT races. It is alleged that teams agreed to the expansion on the basis that all future 2017 WT races (old & new) would only involve 12 WT teams per race except Grand Tours and major Classics. The UCI announcement suggests all old WT races will require all 17 teams to attend and 10 teams to attend the new WT races. Depending on how this pans out there may need to be a change of regs to allow Conti teams to ride WT.
That's great - thanks. I'd seen this 'compromise' about old vs new events as well, let's see what happens. Anyway, race going live on Eurosport shortly, with no world tour teams I don't think :-)