The vote to release Tapestry version 5.0.15 is under way. This is the release candidate. Once it's available, we'll give it a few weeks of exposure (while I'm in Europe) and then, barring any unforeseen critical bugs, we will vote it up as the 5.0 GA release.
I think there's also room to optimize the server-side further. I have some ideas for limiting the number of render commands needed to render a page, and limit the amount of work wasted on event notifications that have no listener.