1. Don't believe the pundits of RAG. They never implemented one.
I did many times, and boy, are they hard and have so many options that decide between utterly crappy results or fantastic scores on the accuracy scale with a perfect 100% scoring on facts.
In short: RAG is how you fill the context window. But then what?
2. How does a superlarge context window solve your problem? Context windows ain't the problem, accurate matching requirements is. What do your inquiry expect to solve? Greatest context window ever, but what then? No prompt engineering is coming to save you if you don't know what you want.
RAG is in very simple terms simply a search engine. Context window was never the problem. Never. Filling the context window, finding the relevant information is one problem, but also only part of the solution.
What if your inquiry needs a combination of multiple sources to make sense? There is no 1:1 matching of information, never.
"How many cars from 1980 to 1985 and 1990 to 1997 had between 100 and 180PS without Diesel in the color blue that were approved for USA and Germany from Mercedes but only the E unit?"
Have fun, this is a simple request.