Evidently, the first leaked ROM from a true and true Windows Phone 7 device has made its appearance.
We say evidently, but perhaps it should be supposedly since as of now, we don't have any proof of anything besides a file. This does come from a Chinese site and spoofs (cough, HD2 running WP7, cough) are a plenty these days. So grain of salt, lets not all believe it quite yet, yadda yadda.
Information is sparse at the moment as the XDA folks sort through the information and decide what the next step will be.
What is known so far is this:
Model: HTC Mondrian (Cingular USA)
So no shocker there that HTC will probably be the first to market with a WP7 device. AT&T may be a surprise for some, seeing as they have not been exactly embracing of anything Windows Mobile as of late.
Download-mirrors for the ROM can be found here, though we're betting they won't be of much use to many. And no, porting this to your Touch Pro 2 or HD2 probably won't be an immediate possibility, so don't get your hopes up just yet.
Update: Becoming more legit. Da_G (his rep is quite high) has posted this:
After further examining the file, there is indeed an IMGFS inside, the D000FF format appears to be a new "store" type of .bin, will need to figure out the format for it to pull out imgfs (because just cutting in a hex editor gives you some invalid data)
Also, IMGFS is compressed with XPH (rather than XPR or LZX as we're used to)
[XDA via @Conflipper]