There may be several reasons to upgrade bugzilla [1], but the one I consider important is the new webservice which is a REST-interface, making it easier for scripting on the client side. [1] https://www.bugzilla.org/releases/5.0/release-notes.html#v50_feat
I would love to do this upgrade and have run through it but Testopia isn't ready. Please see https://git.mozilla.org/?p=bugzilla/extensions/Testopia.git to review the state of Testopia. It is currently working but not yet released. The last time I worked with the Testopia authors they needed more QA and more beta testers. Do we have resources to offer? Is the QA team willing to sort out Testopia errors as they occur? If so we could proceed otherwise this will be blocked until the next release.
adding José to the bug, he's one of the main users of Testopia.
setting it to future, expecting that bugzilla releases the version. The compelling reason for doing this upgrade is also gone given that a test report tool is in the works replacing the need for testopia's advanced features.
After a short discussion I intend to begin the upgrade to Bugzilla 5 soon regardless of Testopia. If needed we will keep the Bugzilla 4 instance running for testopia use only at testopia.yoctoproject.org and disable adding or editing bugs there.
Almost 7 years later the upgrade is complete and the REST interface is available. Testopia is long gone though.