"Coinbase Index Fund will give investors exposure to all digital assets listed on Coinbase’s exchange, GDAX, weighted by market capitalization. If a new asset is listed on the exchange, it will be automatically added to the fund."
For now, investing in Coinbase Index Fund will only be available to US-resident, accredited investors.
https://blog.coinbase.com/announcing-coinbase-index-fund-3925fbf548db