A gang hideout takes a significantly more amount of time and planning to make than a gang gunskin. Its value is so low because when it was added, gang alliances weren't a thing so it actually took continuous effort to base for that amount of hours
I'd argue that they would become more active once this change is made. Obsidian is already at 35k hours/ are close enough. There would be no more rewards for them to go for with 35k being the cap. With bases separated, more gangs will reach 10k hours so maybe initially it might be slightly bare, but I guarantee you competition in those bases will only continue to get higher as time goes on.
P v P can get their reward added if they can have it finished before this change is added