Yeah this bothers me too.
IPv4 addresses are rare these days and providers start to ask for money if you want more than a few or even one.
So, I thought on my new server I'd just use an IPv6 address for the service console and use the IPv4 addresses for the VMs where needed.
Since the provider wants me to use fe80::1 as the default gw and ESXi doesn't let me, ...., well you imagine the rest.
Have there been updates in more recent versions of ESXi?
Or are there workarounds?
At VMware the issue is internally linked to PRs and is being tracked by product development.
There are good chances that this will be fixed in the next major vSphere version (which is in public beta right now).
I am not aware of any workarounds.