Whilst I have no time for JRM, this line of argument is a load of nonsense. Working in the finance industry, I can assure you that if it were that easy, we'd all be millionaires (spoiler - I'm not!). How exactly do you think he'd 'make a killing'? There are thousands of traders, analysts and algo traders all out there to ensure that any potential gains are hoovered up pretty quickly. I can also assure you that there are very, very few people working in the finance industry who see any potential gains from any Brexit scenario.
Based on JRM owning 15% of shares at SCM, he has had a £11m windfall in the last two years from SCM alone. A significant amount of that has come from Eurozone investments.
Anyone can make money from lucky trades in the short term. Clearly you've not seen his more recent performance.
He's been doing badly for some time, it is true - but I thought he was holding a large short position which will only (truly) pay off when the pound gets to parity with the dollar?
Odey and his famous "short the UK" position?