Maybe the OP will respond and explain his need.
That's what I need, in order to help I'd really need a full explanation of the problem you're trying to solve and the full setup, not just the small part of it around "sharing an IP address" - I need to understand the full picture to give advice.
For what it is worth...
Some time ago the Internet went from the use of a four byte IP address to the use of a six byte format. I am still not sure why this was done. Many web servers already had in place a way to separate different computers and customers in a complex wide area network. And I never understood how that worked. It was possible, somehow, to identify everything on the whole wide world. It blows my mind.There must more than a trillion things on the world wide network.
It's not particularly related to the original thread but I presume you mean the move from IPv4 (32bit addresses) to IPv6 (128bit addresses). This is because we have literally already run out of new IPv4 addresses - there are less than 4.3 bullion total possible IPv4 addresses, sounds like a lot but when you factor in the number of people and internet connected devices, it's not that much! This is why your home connection will likely have a single public IP address and then use NAT to translate traffic to/from devices on your local network which all have private IP addresses (192.168.x.x, 10.x.x.x.etc). Then with the current address exhaustion issues, ISPs are finding themselves not even having enough addresses to give one per customer and instead are using CG-NAT to share a single public IP address across multiple customers.
With IPv6 there are 2^128 addresses (over 340 undecillion whatever that is). The idea being that each customer should get at least a /64 subnet which gives 2^64 addresses (over 18 quintillion) with larger sites easily being able to get a /48 subnet giving 65,536 /64 subnets. This insane number of addresses completely removes the need for NAT and things such as private IP addresses, every device will have its own globally unique address. Before I broke the config (really need to get around to sorting it one day) my own home network had a full /48 subnet of IP addresses (2^80 or over 1 septillion addresses) so let's just say there was more than enough to give every device I own a public IP!