How would it make markets more efficient?
If a market was 100 % efficient - a given stock or the market as whole would always be correctly priced with random fluctuations around a given price and should only be re-priced upon new information (and quickly so). And if the price of a stock rose too high - there should be informed investors/traders who short sell that stock/index in order to bring it back to 'fair value'. In theory...
2020 and the fact that market prices trend should convince most that markets are not efficient.
The way it looks to me right now is that we have a lot of people who simply buy index funds at the end of every month with no perception of what they're buying and why they're buying other than the belief that stocks always go up in the long term. To me, it seems like this makes sure there's always a bid in the market and that it can easily inflate stock prices far above 'fair value'.
And given all traditional methods of stock valuations I believe stocks are very much overvalued now and have likely been for a long time.
But maybe those valuation models belong to the past and I suppose they never where very accurate to begin with.
Just my humble thoughts from a short term trader who have more than enough to keep up with the daily gyrations of the S&P.