What happens if the ECB adopts Japan’s de facto target of zero (or even negative) interest rates?

The ECB seems to have switched to a de facto target of zero or negative interest rates, all the while officially continuing to target inflation. What are the implications of this type of monetary policy, which is already in place in Japan? The money supply is no longer controlled (since it is set at the level needed to keep interest rates zero) and may therefore increase without limit; There is no longer a crowding-out effect (an expansionary fiscal policy no longer drives up interest rates); As demand and supply shocks can no longer be absorbed by interest rate movements, growth and asset prices become more variable.