Frankly, there is no perfect supplement/ingredient. It depends on the goals and training state.
1) Creatine dosing is often loaded or washed out, depending on the needs of the athlete. Throwing it in a mix guarantees that you're narrowing your market.
2) It depends on the type of workout, the length of workout, whether I consumed anything before or during the workout, and when my next workout is, and what type my next workout is.
In general, I will consume some form of carbohydrate, and I'll only focus on high GI if one or more of the following apply:
a) I'm extremely glycogen depleted (60% or more), requiring more than 250g CHO to replenish.
b) I'm training later that day, and that session is of substantial volume
c) I'm loading creatine (although this only requires about 30-50g CHO in the presence of adequate protein and leucine)
Otherwise I'll just have some sweet potatoes and a buttload of veggies as my CHO. Maybe a banana if I'm exhausted.
Obviously protein will be included. Whether the goal is an insulin spike, muscle protein synthesis, or glycogen resynthesis, added protein has been shown to substantially increases all of these markers (although with glycogen synthesis, it's only relevant in the presence of less than 1.2/g/kg/hr of carbohydrate... which is often the case). There was a recent study regarding the amount of protein that can be used at once towards muscle protein synthesis (MPS, I'm lazy). The conclusion was about 20g, but this is assuming that the protein is ingested alone, and it also probably depends a whackload on training stimulus.
If you're looking to maximize glycogen resynthesis (without having a serving contain 100g of CHO) then add whey hydrolysate. It's been shown to be more effective (*cough* in rats...) than whey. [1] If you're ballsy, you can even add caffeine to the recovery drink [2]. The obvious downside of this is that you're eliminating its use as a late-night recovery drink. However, for the very specific requirement of two training bouts (or more) in a single day, it's hard to argue that caffeine would be an extremely useful addition to the earlier PWO regimen. Frankly, I'd say that multiple training bouts (or competition) are the most justifiable use of a PWO drink, and liquid calories are a pretty poor practise for late-night sessions, anyways.
The only other "trick" I can think of whipping out is taking advantage of the lone study that demonstrated improved MPS in whole milk over non-fat. One of the theories is that the vitamin D was the affector, and it only worked its magic in whole milk, since it's a fat-soluble vitamin. Adding fat is another ballgame, however. Little information is available on the effect of dietary fat on MPS and glycogen synthesis, and intramuscular triglyceride levels are really not a performance-limiting substrate.
Also, how do you deal with the ratios? Whether you make 3:1 or 2:1 or 1:1 CHO
ro really depends on the nutritional status of the athlete. For periodic competition (e.g. a fighter), 3:1 is probably the best bet. For training, the ratio will depend highly on the goals of the athlete as stated above.
Then you've got insulin secretagogues, absorption competitors, metabolites (I think I covered all my bases here), and all that other crap you could throw in there. Hell, cinnamon (Cassia) has a compound that mimicks insulin.
The more I think about it, the more I think that pre-made cover-all recovery supplements are horsecrap. Of course, that doesn't mean it won't sell. People buy horsecrap all the time! You might be better off cornering a niche market and making something suited very closely to their needs than trying to compete with the well-established big-name ubersupps. And no, "athletes" are not a niche.
Maybe an ultra-low-calorie low-carb pre-workout drink (minimal GI effect, maintain muscle mass, spare glycogen?).
[1] Anssi H Manninen. Protein Hydrolysates in Sports Nutrition
[2] Hawley et al. High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine
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