A samsung galaxy s rom would be very hard, I think. For example, try downloading the galaxy s music apk and installing it on your phone, it won't work or run.
If I remember correctly, the samsung roms only work on samsung devices due to drivers and etc.
The Kernel is good enough, I think it's practically the best we can make out of our hd2's also. when you say 12 hours, as in 12 hours of what? Video? impossible. Gaming? even more impossible. Web browsing? I think I can do it already with my hd2. Standby? Obviously possible, 8 hrs of standby and only lost 3%.
Now 12 hours of gaming/video would be possible if you had the extended battery.
An app that has been released for the general android market should work on our phones.
The ram is as it should be. The desire has the same amount of ram as our hd2's, yet it doesn't show 576 for full ram in system information; so it just says the system is reserving some of the ram for system processing. Which is the same case for us hd2 users.