One remark. Kea doesn't have some of functionalities provided by ISC-DHCP. If you use a lot of dhcp-eval and make decisions based on different dhcp options content kea is still a no-go since there is no workarround. Usually at ISP level dhcp is one puzzle of much more complicated system.

I tried if few times and every time I stuck on something and messagefrom developers was: this isc-dhcp feature is not supported. This was huge national scale ISP and bypassing those limitations means a lot of $ to adapt surrounding systems providing input to isc-dhcp LDAP DB in its own config style.