It really depends on the situation, SNMP is faster and more reliable than WMI overall however there are some things as you know that WMI does better so a balanced mix is better. We've also run into issues when WMI would overtax the RPC service and randomly reboot the frontends so you need to pick and choose where to use it and effectively. So for example lets say you have an exchange cluster what we do is monitor all the servers themselves as SNMP and then we monitor the cluster IP as WMI because its better with mount point monitoring so we'll only monitor the mount point drive space via the WMI node. This way not only does it properly pickup the mount points but if the cluster moves servers it doesn't change the monitoring of the drives.
Keep i mind also with the introduction of powershell in 2008 its still faster for remote code execution and querying the WMI database so thats a better route. WMI is slow and kinda clunky still and also has issues with malformed packets over public netblocks and certain CISCO equipment. So overall SNMP is still the best option for base server monitoring but WMI has its benefits.
Almost 2 years ago I had the privilege of working in a large environment where I could really test out the impact of such questions. The result is chronicled in this thread: Re: SNMP vs WMI polling - pros and cons as well as this document: https://thwack.solarwinds.com/docs/DOC-170788.
As for your question about support, while MS says they aren't supporting it there's a big distance between a corporate announcement and reality.
Mainframes are going to die out soon too, did you hear? I've been hearing it for all 25 years I've been in IT.
Snarking aside it's a worthwhile consideration. I hope the two links above help. Keep us posted as to your decisions.
There are a few small notable differences with windows vs snmp for windows machines.
Long term I agree 100% with adatole , in that basically SNMP support is never likely to go away and always has it's use, depending on the environment.
I'd point out some stuff from his own doc that tend to lean towards favor of one version vs another:
SNMP: reboot state is based on SNMP service itself, allows gathering of network topology, negligibly more efficient
WMI: WMI polling means everything SAM does uses WMI properly out of the box, too (such as all the nice manage nodes stuff - log viewing, service management, etc).