ISPs buying in were OpenNIC's stumbling block (as no normal user is changing their default DNS), ultimately that is why OpenNIC never took off.
The only way an alternate DNS could become popular is if Apple, Google or Mozilla (assuming a resurgence in Firefox popularity) were pushing an alternative DNS.
OpenNIC could work if there'd be an easy way to instruct e.g. dnsmasq and dnscrypt-proxy to resolve only certain TLDs using only OpenNIC, I'd definitely have it enabled then.
The only way an alternate DNS could become popular is if Apple, Google or Mozilla (assuming a resurgence in Firefox popularity) were pushing an alternative DNS.