VMware has announced that the next number version (not update) will be the last version to have a Window vCenter version, vSphere Web Client (Adobe Flash) and support for old Linux style /O drivers.
vCenter on Windows
VMware introduced the vCenter Server Appliance (vCSA) back in version 5.0.
I did not use vCSA version 5.0 and 5.1 at my customers since there where some challengers with this versions.The main was that there was no support migration from the Windows version to the vCSA.
With version 5.5 there still was some challenges, for example the disk layout, where the log partition was part of the 1 disks, and was not easy to extend. There was not an official support migration from Windows vCenter, but there was a Fling.
With version 6.0, I recommended al my customers to use the vCSA and migration was supported (except for the VMware vSphere Update Manager (that only was a Windows application). The disk layout changed the vCSA got 11 disks, the first a traditional partition containing the root partition and the other disks are LVM partitions, containing for example, log, different database parts, and this can be extended as needed.
vCSA 6.5 now has all vSphere vCenter services including the vSphere Update Manager, and all can be migrated. this version got 1 extra disk for the vSphere Update Manager data.
I have been migrating almost al my customers from the Windows version, starting with version 5.5 and using the migration fling. a few of my customers are still using the Windows version, mainly because they don't have image based backup, and the fact that the backup in vCSA 6.5 can't be scheduled from the interface. You can do a scheduled backup using "cron" and a script.
See the official blog about this here: https://blogs.vmware.com/vsphere/2017/08/farewell-vcenter-server-windows.html
vSphere Web Client (Adobe Flash)
The vSphere Web Client that is based on Abobe Flash/Flex, and did never deliver the expected flexibility, performance and reliability of the old vSphere C# client.
This was introduced in vCenter 5.0, but was very limited in function and very slow.
Version 5.1 and 5.5 they add more functions, but the performance was still very bad. With this versions I started using it, because there where thing you only could do in this, but my preferred client was still the vSphere C# client.
With version 6.0, they did do some optimizations, but it was still slow. With this versions I started switching and now i used the 2 client something like 50/50.
One of the problem was that all version from 5.0 till 6.0 did not look like the old vSphere C# client, and you had to spend time find out where do things, that was different from the the vSphere C# client.
In 6.5 they made a big change in the interface, so it now looks more like the old vSphere C# client, and is much faster. but we also got the new vSphere Client (HTML5),
See the official blog about this here: https://blogs.vmware.com/vsphere/2017/08/goodbye-vsphere-web-client.html
vmkLinux APIs and associated driver ecosystem
For the most parts, this will not be a change for VMware administrators, since VMware has been using there new Native drivers from version 5.5, and for the most part this have just worked, but in some case you may have had to change back to the old still drivers.
See the official blog about this here: https://blogs.vmware.com/vsphere/2017/08/vmware-plans-deprecate-vmklinux-apis-associated-driver-ecosystem.html