We do not usually have competitions broken down by hours in level 4 and above. It is usually done by age only. You would be surprised, but a lot of the time kids on less hours do just as well if not better than kids who are on twice as many hours. A great deal has to do with how those hours are used and the natural skills of the gymnast.
As I mentioned with level 1-3 clubs who do very low hours with their level 4 and above kids usually hold their own competitions and only invite other clubs who do lower hours, there are lots of these comps available so they still have a busy competition season without ever going in any of the sanctioned competitions.
But generally level 7-10 is not worked on those clubs who do lower hours, most cap their programs at level 6 and then the girls move into other fields like coaching, cheerleading, acro, aerobics, trampoline and so on.
No doubt there will exist a gap for those gymnasts who reach level 7-10 and are not able to commit to the high hours required, and it is quite likely that these kids will be absorbed into other gymsports (which is not the intention of the WAG SMC).
But in my state, with these new rules, more kids will stay in WAG longer, more kids will compete and reach higher levels and more kids will be able to do level 7-10 as we currently have no state system. But perhaps in some other states it will be less kids.