Let me give a different perspective on the turbo rule you propose, and why it really isn't saving anyone any money.
Turbocharger: The vehicle is limited to a single turbocharger; the inducer bore on the compressor housing may be 2.6”. The inlet will be measured using a 2.65-inch plug or internal calipers. Bushing from any larger turbo size down to a 2.6 turbo is PROHIBITED. A stock map width enhancement (MWE) groove is allowed. No MWE groove will be allowed that has a width greater than 1/4 inch. All provisions allowing air to the wheel other than via the bore and the MWE groove are prohibited.
Based soley on this the competitor have a few options;
1. A true 2.6(66mm) compressor wheel with a standard MWE groove.
2. A turbocharger with a large native wheel and an MWE groove in front of the wheel.
3. A protrusion charger of any frame ie; Borg Warner, Garrett, Holset.
Anyone that wants to compete on a larger scale will buy a protrusion charger that fits other organization's rules. So in essence you are only saving the people money that only pull with NADM or FPP. This is great for those two organizations, but also limits the competitors as they will not be legal for PPL or BOB/COTPC events such as TS, Platte City, Scheid, etc.
Now here is the problem, what you have allowed is; protrusion chargers, deck plates, duals, and open drive line, all in the same class. Remember, it's not about what is written in the rules, but more about what isn't written.