I'm going to be very interested to see how this reclassification impacts the price of REITs. I'd imagine that capital inflows are going to cause a spike in prices.
Come tax time, lots of investors in Financial Index Fund will be in for the surprise, a larger capital gains unless Financial Index Funds decide to spin off REIT holdings as a separate REIT Index Fund instead of selling REIT holdings.
The new GICS sector could bring some new attention to the sector. This probably will affect small cap more than large cap as the generalists take a broader look at the sector. Many have invested in the large caps for a while just to have some exposure. There have been rumors that general stock managers have underweighted the sector overall as it was a part of their 'financial' bucket, but unlike the traditional financial stocks. However, I wouldn't expect money rushing in or out. If there is any price drop over the next couple weeks I would expect it is due to expectations around the Fed rather than ETFs selling.