But it's all relative, since you would be looking at how many year's worth of tax revenues could be monetised.

Such a land-backed State issued currency would principally be domestically acceptable or 'fungible'. Note here that I do not advocate any issue of currency by a State, since I regard State intermediation as just as much obsolete as private intermediation.

I would expect a currency based upon energy - and if an intermediary State is involved, upon a carbon levy/tax - to be another currency acceptable domestically. This would also be fungible beyond a country's borders within a suitable international clearing union.

But there's a difference between a currency - eg money's worth - and the value standard by which currencies are exchanged on credit terms.

Unfortunately the deficit-based currencies we are used to are not based upon tax revenues at all (except bank notes and coin) but are privately manufactured credit objects with very little value behind them at all.

"Any economic unit can emit money. The serious problem is to get it accepted" Hyman Minsky