You'd be more apt to answering this than I would, but I'm curious about the tradeoffs in heat and weight between running two turbos vs one. Your points about the coolant inlet are totally valid, but what about IATs and actual heat generation with two smaller turbos vs one? And I see you've just released your own line of turbos, which is awesome, but call my crazy, I have a huge fear of running anyone's twins on track because of all the horror stories, not to mention the pain in the ass install. A single is way easier to service, and backed by a company like Garrett, BW, etc..
IATs are primarily a function of boost, compressor (adiabatic) efficiency, and intercooler effectiveness, and have nothing to do with the whole single vs twin debate, and everything to do with having the compressor wheel(s) properly sized for your application. You are confusing IATs with in-cyl temp rise caused by high residual gas fraction from running a EMP/TIP (high backpressure/boost) ratio - an issue with older TT offerings using stock turbine housings, and certainly not applicable to mine. I understand your reliability fears given all the horror stories out there, but I'm hoping that my use of OEM TD04 turbine wheels + good QC/attention to detail should make this a non-issue. Time will be the ultimate judge I guess, although in the final analysis everything fails eventually. I have an Evo X customer here who is on his 3rd GTX3071R... Finally, I don't see why a bottom mount single turbo would be "way easier to service", sure you have 4 less oil/water line connections to worry about, but accessibility is still hindered no?