I can see that in previous versions of TFS Build it's been possible to add a custom section to the build summary screen, but I've been unable to find anything for 2015... has anyone done this for the latest version of TFS Build?
The new build summary displays on the web portal. Currently, these customizations are not supported.
You can submit it to User Voice site at: http://visualstudio.uservoice.com/forums/121579-visual-studio