As I said earlier, this will lend a ton of legitimacy to Bitcoin being a viable trading commodity to big financial players, which is basically what the quote is saying. Up until now, in the major financial world, BTC has been thought of as the cute thing people trade while sitting in their mom's basements, but now being thought of as "a new asset class" opens up a lot of new doors and opportunities. Think of these index additions much the same way you would of a celebrity endorsement of a product, but in this case it is a financial heavyweight endorsement.
Now this doesn't mean BTC will skyrocket and be traded everywhere overnight, but it is certainly a major step forward in that direction. Once you start to get the option to choose BTC as one of your Fidelity or Vanguard retirement fund picks, then you will know we have arrived.
Bitcoin is still not liquid enough for the big financial players - but what this will allow them to do is "trade the index" outside the bitcoin space. I wonder how many will take it up... My guess is that they'll wait till the halvening is over and also look to see whether Satoshi starts moving his coins.
Agreed, the takeaway is that this is the beginning for Bitcoin in the mainstream financial world. It took 6 years to get this far, it will probably be another 6 to get where there is serious liquidity for the big boys. But I think by then there will be more alts coming along for the ride too, so even though it starts with BTC, I think eventually there will be a cyrptocurrency index fund that tracks the top 10-20 coins. Something like the Dow but for crypto.
Maybe they could call it the Satoshi index or something.