I'm looking for a way to migrate Windows based vCenter Server 6.5 to the new VCSA 6.5. I know currently you can only do this from 5.5 or 6.0u2, but was wondering if there will be a utility or KB for doing this in the future or would the best option simply be to stand up a new Platform Service Controller and vCenter Server with the appliance and then somehow copy the database over?
At this point in time as you have noted, VMware don't support a parallel migration from windows VC to the VCSA. This is something that they appear to have received a lot of feedback on and are likely working on, but of course won't commit to a release date for such a utility.
So at this point in time your option is to stand up a new VCSA based deployment and then migrate hosts, VMs, roles, permissions, plugins etc across to the new vCenter Server. There is no way to bring across the database itself, so during this type of migration you will lose some statistics such as historical data.