What that means is that as custody solutions are currently present only for Bitcoin, it makes sense to invest in Bitcoin at first. Later, though Coinbase and other large players will develop and release similar products for institutions that allow them to invest in other cryptos. Whether they will be rolled out and deemed acceptable by institutional investors before the next big bull run hits is questionable. It makes a lot of sense to focus on BTC now. Once BTC has peaked, it will be a good idea for retail investors to diversify into other cryptos. All the boats will rise because of the influx of institutional money but Bitcoin will obviously be the first one to benefit.