Frequent commenter Don Johnson, an infill developer, sent me the picture below, which nicely illustrates how the McMansion regulations actually encourage the construction of massive duplexes.
Requiring the units to share a common wall guarantees a massive structure. The building envelope eliminates any interesting architectural variation and forces every structure to the middle of the lot. Mandating side-wall articulation means a jagged, jumbled design.
The worst provision is probably the common-wall requirement. The developers I've spoken to say they'd prefer to separate the units, using the garage as the connection. (Many pre-McMansion duplexes have this form.) This would result in two smaller units rather than one giant structure. But the McTask Force apparently felt developers were circumventing our anachronistic lot-size requirements, so they decided to stick us with these hulking structures -- duplexes guaranteed to clash with the existing stock.
Thanks, Task Force. Thanks a lot.