I've been thinking about turboing a 1.8 or 2.0 T4 (if 1.8 then I can run the 1.8T badge!). I dont know much about or pretend to know much about turbos, but I think that a smaller displacement T4 with a moderate turbo would be an amazing daily driver car. I'd do a blow-thru with an intake hose from the outside to the firewall, where the turbo would take its air from (enclosed box), and maybe an air/water intercooler.
Either way, I think that the reliability factor of the T4 coupled with the power making abilities of the turbo AND the T4 would make for a reliaboe, powerful turbo'd street engine.
It's a different approach, especially if you dont have the engine building skill. You could fab up a turbo system to a stock engine for the same $ as buiilding a bing N/A engine.
Oh, wait.... that wasnt the question...
I sat if you are going T4, put all available funds into the T4. Why spend money on a temporary engine? Unless you can figure a way to use the turbo on the T4, don't do it.