I was wondering the same thing myself so I started to do a quick calculation for one particular index fund.
Total Market Cap for TSX Composite Index = $1,551 billion
ARU Market Cap = $1.26 billion
... which means that ARU is 1.26/1,551 = approx. 0.0008124 or .08124% of the total market cap of the index.
Just to pick a fund, TD's Canadian Index Fund has $850 million in assets under management so they would need to pick up approx. $850 million x 0.0008124 = $690,540 of ARU stock to get to approx. 0.0008124 of their total assets being ARU stock (not sure how this works exactly to be honest with you).
I am not sure how many index funds are out there that would need to acquire ARU stock but imagine that the total for all index funds affected would be pretty significant.
If anyone has another take on this I would be interested in seeing it.
Also wondering about timing ... how much time do funds have or would they take to add new additions to the indices to their portfolios?
