Basically these are things the other grading companies have screwed up...
1) Get right the designation with respect to business strike coins vs 1965-1967 SMS coins and 2005-2010 Satin Finish coins. This is really important. There's lots of mistakes in another TPG's holder. This has messed up the pops, the registry rankings, and people have paid $100s or even $1000s for coins that should be worth almost nothing.
2) Get right what constitutes a major variety, and hence should always be designated. And if a variety is missed at the start, and added later, make sure you know which is the rarer version among those generally submitted. One example is that pcgs did not designate 1939 nickel reverse types, despite the quite obvious difference in how the steps look, until about 2004. Then when they did start designating them they lumped all the existing undesignated ones with the R38 despite that in gem+ full steps the R38 is rarer (much rarer for 39-p, but perhaps in general BU R40 might be rarer). People still "cheat" and register or try to sell R40 coins as R38s because it's undesignated. The best thing would have just to have gotten it right from the start.
3) I've mentioned it in other threads, but will again... I strongly recommend 5 steps should constitute a full step Jefferson Nickel (up through 1990). Having both 5 and 6 step designations would be great too.
4) What makes up a basic registry set vs a with varieties registry set etc. There will be lots of different opinions on this from different people, but just a few examples of things pcgs did out of the blue that angered a lot of people were...
a) Suddenly added the 1958 DDO cent to the Lincoln Cent sets w/major varieties knocking almost all participants who had a 100% complete set down to a 99% complete set. My opinion would be to add coins like this as an optional bonus coin.
b) They (mistakenly in my opinion) were allowing satin finish coins in the 1999-2008 state quarter set and then suddenly changed it (fixed it imo) and only allowed business strikes. This really angered a lot of state quarter collectors and perhaps is the reason this set was so dead for so many years. It'd have been better to just have had it right from the start. But I also note an inconsistency as the other denominations still allow Satin Finish coins in their 2005-2010 spots (they shouldn't imo, satin finish should only be in the w/varieties).
c) They one day removed the 1976 Ike types from the basic set. These are "types" and not varieties in my opinion (ie major intentional changes to the design of the coin) so this seemed like a mistake to me. But like the above issues I think it was the sudden out of the blue change that angered people.
I'm sure I have more but have typed long enough for now. Please feel free to add your own things that you hope cac gets right.
The only thing I care about is for CACG to define their standard, be willing to display that standard to everyone who wishes to see it, and stick to that standard instead of kneeling to the market pressure.
Could you explain how CAC handles original toning versus corrosion. Original toning can hide a lot of problems, IMO.