Considering in the UK you can get sim cards with 10GB or so of data for pennies I'm a bit surprised I don't hear much about people doing old school self hosted

Considering in the UK you can get sim cards with 10GB or so of data for pennies I'm a bit surprised I don't hear much about people doing old school self hosted direct access stuff over ipv6. Would there be much of a security risk if you had a dedicated device on its own network that doesn't actually directly communicate with anything else in your home?