I thought about this when researching buying and customizing an enclosed cargo trailer that would be towed behind the motorhome I'm planning to get. This is intended for boondocking, where I would locate a large (100-300 gallon) tank between the axles of the trailer and have a Jabsco inline waste evac pump (similar to a macerator pump, but doesn't grind up the waste, and uses a diaphragm method, so it can be run dry without issue) for dumping the tank.
The advantage of this is that with the weight between the axles, the trailer's stability was fine regardless of how full the tank was. With a vent on the roof, the tank wouldn't cause any odor issues in the cargo trailer, allowing the trailer to still be used for sleeping in case of emergency.
However, the disadvantage I encountered is weight. A 200 gallon tank is a ton of sewage.
My compromise (and this trailer is slated to be worked on after I get a decent motorhome) would be specific tie-downs or ramps so I can roll 2-4 Barker 42 gallon totes into the trailer. The advantage of this is that when that much waste capacity isn't needed, the totes can stay at home, and if I can't really move the trailer, I can roll the totes around.