Audi with the current engine rules would make a fantastic entry into the F1 arena, whether that be as a full team or just an additional engine supplier.
But they need to produce a hybrid, V6 turbo engine that they can race before that point. Oh, look, they already do that for their road cars so just performance improvements needed. Oh, hold on, they already do that under Audi Motorsport (have been known to take their 3.2l V6 up to a turbo hybrid engine that puts out 750psi plus with a road life of over 100,000 miles so not a big leap to get one that last a few thousand miles with over 800psi).
But Audi need to improve their fuel economy to the point they could survive in the low fuel consumption world of F1. But hang on, didn't they just do that for LeMans and their advantage is not the power they can produce but the fuel economy meaning less stops in an endurance race?
So they already invest in all areas that F1 would need, would just need leadership and combining of all the areas into a single engine. But here comes the big thing that means they will not do it under the current rules, they want to do all this on Diesel engines not petrol because they can then apply this to their road cars and make money from it. All the Audi sports car tech that is developed for any Audi race entry will eventually appear on road cars and be relevant to normal road usage. They had KERS systems that used your breaking energy to improve fuel economy during acceleration years ago, they drive the fuel economy figures in sports cars to the point that they now produce a V8 road car that can achieve 40+mpg on the motorway, but still accelerate like a V8 sports car. Nothing in F1 is new to them and the rules are so restrictive over fuel consumption, fuel type and engine development that it is not worth their effort when they make bigger and better advancements in other sports series that they are already making money out of.
Unless the engine and fuel rules change don't expect to see anyone from Audi making a big announcement soon, would just be extra money down the drain with no benefit gained from it...