I find this completely fine. I don't see much (if any) upside in migrating a large existing network to anything new at all, as long as the currently deployed IPv4 is an adequate solution inside it (and it obviously is).
Public-interfacing parts can (and should) support IPv6, but I don't see much trouble exposing your public HTTP servers (and maybe mail servers) using IPv6, because most likely your hosting / cloud providers do 99.9% of it already, out of the box (unless it's AWS, haha), and the rare remaining cases, like, I don't know, a custom VPN gateway, are not such a big deal to handle.
Public-interfacing parts can (and should) support IPv6, but I don't see much trouble exposing your public HTTP servers (and maybe mail servers) using IPv6, because most likely your hosting / cloud providers do 99.9% of it already, out of the box (unless it's AWS, haha), and the rare remaining cases, like, I don't know, a custom VPN gateway, are not such a big deal to handle.