Sometimes our computers have updated packages and systems, but the CI services have outdated ones, and we would like to use new third parties APIs, for example GTK. The policy of some systems (e.g. Ubuntu) about libraries stability breaks some modern developments. I would like to get continuous building using libraries with suitable versions. I know we could update the system, but Ubuntu 12.02 has some limitations (more than 3 years old). I think providing options to choose distro versions would fix 50% of the problems.
On the other hand, the problem of versions APIs/ABIs shows me how to build more portable systems. Well, what do you think?