What about those without IPv6 running?
Anyway, in the enterprises I've worked in the past decade - of course, another anecdote - not once has anyone ever specified an IPv6 address of anything. Inside the organization or outside of it.
everything fit's nicely in the 10.0.0.0/8 range
in my many decades of enterprise infrastructure, no-one has ever mentioned IP6 either.
why would they, whats the business case?
if you've never run in to this, then sorry, you've not been in an enterprise, you're in a mom 'n pop shop cosplaying as enterprise.
I don't claim IPv6 isn't used anywhere, or even that it's not used a lot.
With subnetting needs, possibly dealing with VPNs to other networks that might use 10./8, ISPs that might use 10./8 instead of CGNAT space (100.64./10), even the total incompetence of some contractors was not reducing how IPv4 was a problem.
And that's before you hit the part where Microsoft products have been IPv6 First since ~2008 and there are entire feature sets that are very interesting to bigger companies (like well integrated always-on vpn for laptops) that require working v6
Except during a merger/acquisition and both companies have 10.0.0.0/24 in their OSPF or IS-IS topology.
Except for when it doesn't.
If you just use that space as a flat range, it is almost certainly more than enough. But if you split it up in multiple levels of subnets, you can run into difficulties balancing having enough subnets and having enough space in each subnet.
IPv6 is much more stable on what you can use. fc00::/7 is actually private use.
In short: The market has already decided and it's private. It's far from the first time an unofficial arrangement is the de facto standard.
If you deploy IPv6 correctly, you shouldn't have to disclose IPv6 addresses to users inside or out -- DNS keeps the address literals abstract, hidden from users.