Actually direct injection thus far has proven to be a godsend for boosted applications.
Because the pressure of the fuel being injected and the size of the injectors, there is HUGE headroom in the stock fuel system. Think about it, the fuel is being injected at an immense psi since its being introduced right before TDC and the spark event so it has to have alot of pressure behind it. Now you add 7, 14, etc PSI. This amounts to jack shit compared to the force pushing the fuel in.
The other vehicle love interests I have are genesis coupes, the 13+ are direct injection (both 2.0t and 3.8 v6). The v6 guys are throwing on turbo kits and only seeing menial increases in IDC in order to match proper afr's. The added volume of air just doesnt make much of a difference compared to whats already in there and whats being injected.
But a lot of that has to do with how much headroom the manufacturer designs into the cars. If I remember right the DI MazdaSpeed 3's suffer from an issue where you have to basically choose one or two mod paths and that's it. Basically intake and tune or boost controller and tune and you're out of fuel injector. Due all three and you don't have enough fuel flow because Mazda didn't leave much headroom in the injector design. Pressure plays a factor, but in the end it's all about quantity to make the right AFR's.