The program outlined Sunday by the Basel Committee on Banking Supervision raises minimum capital levels substantially. U.S. regulators said the new rules will provide “for a more stable banking system that is less prone to excessive risk-taking, and better able to absorb losses while continuing to perform its essential function of providing credit to creditworthy households and businesses.”

Yet the Basel III outline, issued two years after the collapse of Lehman Brothers and the bailout of AIG , stops short of addressing one of the toughest questions raised by the 2008 crisis: how much to charge giant banks for the risks they pose to the safety of the financial system.

Researchers have been pondering this long-running taxpayer subsidy to bankers and how to reduce it — a process one investigator calls the $100 billion question. Wall Street expects regulators to decide that the biggest global banking companies, ranging from Citi  and JPMorgan Chase  to Goldman Sachs and Morgan Stanley , must hold capital beyond the higher standards unveiled Sunday.

“One remaining uncertainty is how large incremental requirements ‘beyond the standards announced today’ will be for systemically important banks,” Citigroup analyst Keith Horowitz wrote in a note to clients. “Rules are under debate, and we estimate regulators could impose an additional 100-200bp requirements for these players” — or an added 1%-2% in capital, beyond the 7% minimum.

But for now, the Basel committee said only that it is working on the issue — while noting that higher capital standards may not necessarily mean a bigger equity cushion alone.

Systemically important banks should have loss absorbing capacity beyond the standards announced today and work continues on this issue in the Financial Stability Board and relevant Basel Committee work streams. The Basel Committee and the FSB are developing a well integrated approach to systemically important financial institutions which could include combinations of capital surcharges, contingent capital and bail-in debt. In addition, work is continuing to strengthen resolution regimes.

Though no one doubts the value of coordinated policy, some analysts are betting that the heavy lifting on the too big to fail issue will be done by national governments, not the Basel committee.

“Our hunch is that we should expect to see this more country-by-country,” write Morgan Stanley Europe analysts Henrik Schmidt and Huw van Steenis. “Switzerland and U.K. are the two markets where we would expect this to be hardwired into regulation.”

They note that the giant banks in those nations are very large relative to the national economies, which makes another round of bailouts even less palatable. Ireland is currently dealing with the immense cost of bailing out banks that are large relative to the size of the economy.

And what about the U.S. banks? They have been rallying Monday because of their strong capital positions and the length of the Basel III phase-in period, and the Morgan Stanley analysts suggest the good news may keep on coming.

A strong domestic regulatory push on too-big-to-fail costs is “much less likely” in the United States, they write.