I ran across this quite awhile ago while looking at other projects an thought it was interesting. The BMW N54 engines, have integrated manifold/turbos that are V-band compatible for a downpipe as well as internally wastegated to around 4 psi, plenty to bump power in a little 2000lb. i3. Best way to see how close the primaries are to one another and see if it would be feasible would be to buy a 335i or 135i N54 exhaust manifold gasket and a 2014-2017 Mirage exhaust gasket to compare each against one another, but according to the pics below, they look pretty similar. I don't yet have a Mirage, but thought it may be useful to somebody.
As far as engine management, Emanage Blues (yes blue.....I know the crappiest), has an injector harness or up to 6 injectors, so 3 extra injectors (or less) could be wired and could also be used to eliminate the original fuel cut form the ECU/PCM to extend the rev limit past factory. Basic explanation is to use the extra 3 injector wires (each injector would have 2 injector wires) to each of the already existing 3 injectors and these injector wires would be used to send signal from the Emanage Blue to the injectors after the initial fuel cut. These 3 extra injector wires would need a diode wired into the wires to make sure the injector signal is 1-way and the factory fuel cut is bypassed. Or they could be set up to add extra fuel if needed to 3 supplemental injectors, leaving the stock rev limit intact. Emanage blue is pretty easy to find for $100 these days as most popular vehicles throw it away or use a better management system (such as FIC, etc.).
Either way, just hoping it'd help someone out or somebody may be interested in the idea and pursue it.....