What new fiscal rule in the euro zone?

Most commentators accept the idea that the current fiscal rules in the euro zone (fiscal deficit below 3% of GDP, structural fiscal deficit returning to 0.5% of GDP, return to a public debt ratio of 60% of GDP within 20 years at the most if it is higher) will not survive the COVID crisis. But what should they be replaced with? A complete absence of a fiscal rule would only be conceivable if fiscal deficits were perpetually monetised by the ECB, which is not possible. Moreover, the northern countries, notably Germany, reject such a solution; A "smart" fiscal rule would probably involve: A ban on taking on debt to finance current structural fiscal deficits that are non-cyclical and not generated by investment; But with the possibility of taking on debt to finance efficient investments, with a commonly accepted definition of such investments in the euro zone.