It's a good turn of phrase but people always use it for their crypto projects. https://m.reddit.com/r/dogecoin/comments/32fujo/is_dogecoin_the_gateway_drug_of_cryptos/
https://www.deepdotweb.com/2015/04/13/ziftrcoin-the-future-of-cryptocurrencies/
https://steemit.com/steem/@steempower/steem-the-gateway-drug-into-digital-currencies-for-the-masses