I don't think SNMP is going anywhere anytime soon but I do think that it is slowly getting phased out. More and more vendors we have worked with have moved away from SNMP and Windows is now doing the same thing. When it comes to Windows I find WMI to be better in pretty much all ways except for speed, if MS would address the speed issues with WMI I think it would be great. Other vendors I have worked with have moved to their own built in monitoring tools that allow you to send alerts via email. Then there are the vendors that provide an API and expect you to take advantage of that. You also have storage vendors that use SMI-S.
I can't say why there is a move away from SNMP which seems like a great standard; however, it does certainly seem to be happening. I am glad to be using SolarWinds as my monitoring vendor as they seem quick to adapt to vendor changes in monitoring capabilities.