got to see one of these tr8s in person recently and its pretty cool. not bad, but it didn't blow me away by any means. i can see why some people would like it though. personally, i'm not a fan of drum machines, i'm more of a sample guy...
i heard roland made it with the possibility of adding more emulations of other analog drum machines in mind to it. So while right now it only emulates the 808 and 909 or whatever, in the future they may allow you to add other analog drum-sound emulations to it or something like that. I'm sure this was all covered in the video but I didn't feel like watching the whole video since I got to see someone else using it in person.
still, i see no personal need for one of these at all and won't be buying one.