My prediction for the ACR:

I think that we will see a HP bump to 700 hp. The upcoming Hellcat Hemi is rumored to be a supercharged 6.2L. I think it will have direct injection. Direct injection is now common technology and I think SRT likely has access to some people with very good knowledge in this area at sister companies and suppliers. SRT will probably adapt the pistons and rods from this engine along with the direct injection components (fuel pumps and injectors) to the Viper engine and change the bore size if necessary (as they did when they brought out the 6.1L Hemi).

Direct injection will allow for much better control of the combustion process and will allow for changes to the cam and an increase in compression ratio. This would also require a new head and intake, which means they will probably take the opportunity to increase air flow as they no longer have to worry about keeping the fuel particles in suspension in the intake track. Combine this with new headers and 700 hp is easy and will likely have better emissions and fuel economy to boot.

Add big aero, like on the Gen IV ACR, some Sport Cup tires or the Pirelli equivalent, adjustable coil-overs, TA brakes, and a hardcore package that takes out another 30 pounds for no AC and sound system. I think you then have a car capable of equalling the ACRX time at the Nurburgring and setting a new lap record at LS by several seconds.

I think all of this could be done for not much of a cost increase over the current car. The engine upgrade to direct injection probably has to be done sooner or later anyway, just for emissions in the future. I think this is a very reasonable way to create an ACR that will rival anything else in the world when it comes to track times. The engine improvements would quickly be rolled out to the rest of the Viper line to amortize the costs.

No need for anything more fancy and costly when this would get the job done in a compelling fashion.