Let's encrypt isn't any real new technology. All it did was removing cost and fully automating all aspects of the process. Before let's encrypt certificates had

Let's encrypt isn't any real new technology. All it did was removing cost and fully automating all aspects of the process. Before let's encrypt certificates had to be paid by money. The trouble with IPv6 is the hen and egg. For ISPs it's troublesome as they have to run double stack, till the last site on the Internet is converted and for site owners the trouble is they have to double stack till last ISP converted. Doing anything backward compatible isn't an option as the trouble is I. The 32 bit address limiting number of addresses on IPv4, and any form of increase causes compatibility issues. (Of course one could build an IP protocol closer to IPv4 with just larger address space, but transition costs would still be very similar to IPv6)