The SimpleTest browser that is included in the Drupal 7 core is very powerful and I have found myself hacking in order to use it outside of SimpleTest on a number of occasions, as have others. In addition the DrupalWebTestCase is becoming rather bloated. There is an issue to create pluggable backends for drupal_http_request which could be cleanly done by abstracting the SimpleTest browser. The change would create a clean and more powerful API as well as open up a number of possibilities by having a browser built into Drupal core and thus is something worth working on.
A while back I did some work towards abstracting the SimpleTest browser, not only out of DrupalWebTestCase, but improving/cleaning the code and writing it with a pluggable backend layer. The code is quite far along and just needs a bit more refinement before it can replace the existing SimpleTest browser. The next step would be to replace drupal_http_request or make it a wrapper. After that, areas of core that parse HTML and such can be cleaned up and simplified using the browser.
With a browser in core there are a number of powerful tools that can very easily be added. For instance install and update scripts that can trigger remote servers!! Think of having a single script on a development machine that runs the update script on all specified sites!
Installing via a script can be very usefull not only for the obvious, but also for modules like the Usability Testing Suite and Project Issue File Review that have to make separate installations of Drupal and currently must maintain their own install scripts. Having an abstracted installation script is necessary for testing.drupal.org to be able to function with patches that make changes to the installer.
I plan to work on this further, but have been busy with other projects lately and my recent video card experience. I would like to hear some feedback from the community and possibly recruit some help.