It's not a bad idea. Just one that would be hard to manage without quite a bit of difficulty. With Hypancistrus species, you're not losing much by reducing the footprint of the tank. You can get as much use out of a front/back or side/side divider. Just provide multilevels of caves to mimic a bank or root niche to compensate for loss of footprint. However it's set up, provide a perpendicular current to the orientation of the caves/recesses and they'll find plenty of spawning places. And, with open access, you'll have an easier time maintaining the tank and providing fresh veggie and fruit pieces to augment their prepared diets.