I have an HD2, and this would be a welcome upgrade. The only problem is the T-Mobile exclusivity. The way their service is where I live, there's no chance I'm going to switch carriers.
My HD2 on AT&T is an imported Telstra version from Australia with a custom ROM to work in the US.
I'm still going to get a WP7 device, but unless I find out that something similar is going to be possible for WP7 devices, I'm going to be sad.