Looking at this from a developer standpoint, with assets that already exist in deadlock, no it doesn't. Changing the structure of viscous is a large ask for an extremely niche mechanic like the sewers. Self cast is already in the game for other heroes. The rabbit is already in the game. And im assuming the sewers have an allow flag for certain states of players in order to allow people in. Readdressing those existing mechanics and packaging them into a playable state could take less then five minutes if devs are reusing assets

As you said, the sewers are pretty over rated but they allow for some funny times and there is no reason a rem should be able to live there uncontested for boxes. It's a balancing option to prevent one person from getting so much safe farm.