The general public does not understand futures. It's kind of like options. The instruments themselves are complicated.
The material advantages of Micro's over an ETF, like capital efficiency, ability to fine tune notional exposure, spread risk, and trade overnight are probably too complex to be recognized by the general public. These are the same advantages the Mini's have with respect to the cash market.
I don't think there is a scenario where ETF dominance is threatened. For example, micros will never be a destination for 401k funds.
retail traders will increase their part in the market movement of the future indexes as they shift out of their ETF's over to the Micro-Futures
The micro's are almost completely irrelevant with respect to moving the market.
Total of all U.S. listings is something like $34 trillion. Micro is like $14,000 notional.
In fact, since the US market is 'risk arbitraged' against international equity indexes, the introduction of these instruments, though useful in some ways, is of very little, if any material consequence.
It will probably shake up the 'dealing desk' FOREX business and maybe the binary options, spread betting, and even CFD brokerage businesses. Kind of interesting to see that play out. They are competitive with these instruments in some ways, less so in others.