That topic has been raised on IRC yesterday, to summarize the discussion, it probably won't be changed anytime soon, as it requires active participation from all buildbot maintainers and the according coordination. That doesn't mean it's impossible, but to my understanding a low priority topic with no immediate timeframe attached. Changing build dependencies on the buildbot side is not done easily, it's a change that affects many users whose builds will no longer succeed (the brief requirement of GNU time rather than relying on the shell-builtin still shows its disruptive effects), as well as arranging the host-side buildroot changes with the administrators of contributed ressources.
Disclaimer: I'm not an OpenWrt developer, nor involved in this topic at all, merely trying to report the answer already given to someone else on IRC.