** Shares of trading platform Interactive Brokers IBKR.O rise 4.7% to $65.7 premarket after co set to join S&P 500 index .SPX, effective before markets open on August 28
** IBKR replaces Walgreens Boots Alliance WBA.O in the S&P 500, S&P Dow Jones Indices says
** J.P.Morgan analysts estimate S&P 500 indexer demand for IBKR shares to be 55.6 mln
** WBA is being taken private by Sycamore Partners in a $10 bln deal announced in March
** IBKR moves up from the S&P 400 Mid Cap Index .IDX, utility Talen Energy TLN.O to take IBKR's place
** Pipeline operator Kinetik KNTK.N joins the S&P 600 Small Cap Index in place of TLN
** As of last close, IBKR shares up more than 42% YTD with a market cap of $106.7 bln
(Reporting by Shashwat Chauhan in Bengaluru)
((Shashwat.Chauhan@thomsonreuters.com))