The limits on transaction size have been known since the beginning of Bitcoin. VISA level transaction rates require insanely high block sizes, much larger than those proposed so far. People have come up with many, many different solutions to this problem.
One thrown around a lot is the lightning network [1], but it's not really a "reserve currency" in this case - it's a way to prevent a bunch of intermediate transactions from entering the blockchain forever, but it's based around advanced Bitcoin scripting usage, so it's using Bitcoin for much more than just a backing value.
Keep in mind that Bitcoin currently has a $6 billion USD market cap. Breaking Bitcoin would reduce that to $0. Many people have strong motivations to be conservative with changes...