Here's the only link I've seen indicating WM6.1 for the 750:
http://www.palm.com/us/company/pr/2007/102307b.html
It's old (October of last year) but does say that their will be a release to make the 750 compatible with "Microsoft System Center Mobile Device Manager 2008" to be released in the second half of 2008.
For those not "in the know", compatibility is enabled by loading WM6.1 on the device.
http://www.microsoft.com/windowsmobi...r/default.mspx
So we have an official mention early on with no actual date attached. Hmmm... Reminds me of when they said WM6 was coming soon.