More for single turbo 4 banger/twin turbo 6 type stuff, the point being, minimizing hotside volume can improve transient response. Not really a factor on drag stuff with loose-ish converters.
Agreed, the shorter the better. Some of the modern V8 diesels have the exhaust exiting into the valley of the engine with the turbocharger mounted there to reduce the pre-turbine exhaust volume too.
"Hot V" has a couple of benefits. High end German gas motors are doing the same. Keeps the hot side short, keeps the volume pre-cat to a minimum for catalyst light-off, and heat naturally rises, so keep all the hot stuff high, in the same place. Most of the development now is centered on emissions. If you don't meet the requirements, you can't sell them (unless you are VW...)
This does create a nightmare for coldside plumbing, and separate TB's on each bank can create some torque model challenges.
And there is a "right" size for your coldside volume. It should be large enough to not evacuate and pull a vacuum when you go WOT before the compressor can build boost, but larger than that is just excessive weight, cost, etc.
