If a minimal ui is all that we invision ever having then just keeping jamon and moving the last pages off of jsp seems the best. However if we want to have things like monitoring and trending (stack you and I had mentioned this), a shell (someone at hadoop summit mentioned this), and configuration (we started talking about dynamic configs lately) all on the ui then I think it could be worth it to go to a more modern and adopted framewor
IMO we should keep the built-in pages simple, and expose all the right APIs so that an external "fancy" UI can be built. The fancier we make the built-in UI, the more likely we have bugs in it, and the less likely it'll be usable from command line browsers like lynx (yes, I do that reasonable often!). It also tends to result in cases where we have data that's only visible through the UI, which encourages people to start scraping HTML to gather metrics, etc.
On the other hand, if everything's available via APIs, then we can have an external web UI with all the whiz-bang features we want. The external UI might be another daemon running in the HBase project. I think Accumulo takes basically this approach (theirs is called the "Monitor" process, and it talks to the actual daemons via thrift, as far as I understand)