I too find Market Monetarism interesting. However, I find the discussion around it bafflingly incomplete.

I live in Britain, where legally the central bank (BoE) is supposed to target inflation at 2%. In actual fact, however, before the economic crisis the central bank had inflation consistently running well above its legal target. What it was doing, however, was keeping NGDP growing at approx 5.5% per year - and it had been doing so for over a decade. It was therefore generally thought that, letter of the law be damned, the BoE was in fact an NGDP level targeter, of exactly the kind recommended by Sumner et al.

Then 2007-8 happened, world financial crisis, bank failures, etc. NGDP collapsed despite (1) the BoE attempting to maintain NGDP and (2) the existence of the target. Moreover, despite the fact that the BoE continued its measures, NGDP did not recover to trend, and shows no sign of doing so. What is more, apart from a brief period in 2009, inflation has been well in excess of the BoE's legal target throughout the period in question. At the time that NGDP was collapsing most sharply, inflation was over 5%!

This seems like a direct challenge to market monetarism. If the expectations channel is so effective at determining NGDP growth, how did expectations become unmoored? If the central bank really can determine NGDP, how did it lose control - and note that this is not a situation like the US, where MMs can genuinely argue that policy has been too tight. The BoE allowed high inflation rates and a massive devaluation of the currency (the £ lost around 25% of its value), but still could not get NGDP back to trend. Moreover, despite monetary policy in the UK being much more accomodative than in the US, economic recovery has been much poorer. Why has this been the case? Why has base money ballooned here, like in the US, but unlike in Australia?

I am not saying market monetarism is wrong as a theory, necessarily. But it needs to have something to say about this situation, because on the surface it appears to be a case of market monetarist ideas put into practice, and being a complete failure. However, market monetarists do not seem to have much to say about this, instead preferring to talk about cherry-picked examples - Britain pursued a much more market monetarist policy than any of Israel, Sweden or Australia, and has a larger economy than all 3 combined. Moreover, Australia in particular engaged in large-scale fiscal stimulus of the kind market monetarists say is unnecessary. The old joke goes that macroeconomics is the study of the American economy, and it looks particularly the case here. The issue has particular salience for me because I'm British, but even besides that, if a country puts your ideas into practice and it fails, you need to do some explaining.