I'm pretty sure this is market forces. Glut of savings --> low rates. Sure there are local exceptions and regulatory impacts, but those generally can't stand against the tide, so I'd say it's 95% natural.
> inflation of money supply
Depends on the currency, but in the case of USD, increasing the supply is necessary to avoid deflation, which would seem superficially good for savers, but would be disastrous for economic productivity.
> high taxes on earned income
???
> subsidies to speculators (housing subsidies)
I don't know much about this one, but I think most subsidies are homestead-y (to owner-occupiers and first-time buyers).
Indeed, the article seems blind to capital taxes, focusing instead on income tax. Wealth tax is a pretty alien concept in the US -- I think it would face strong cultural resistance, and cause even more wealth flight to tax havens. And yet, I can see how it would tackle a big part of the problems described here.
It may need to be implemented in a coordinated global fashion to avoid cheating. You'd need the rich nations to do it, with a working enforcement mechanism that spans international borders. That, combined with cultural resistance, sounds hard.
I thought interest rates were kept low to entice those having money to, rather than put it in the bank, invest it, that is: speculate. Problem seems to be that that's not what households did. In many countries, they paid back on their mortgages and put more money in the bank, despite the low interest rates. The science of psychological economics isn't that well developed, it seems.