I have spent a considerable amount of time lately in doing a lot of maintenance: merging patches that implement minor changes and small bug fixes.
I am aiming to finish a few more pending ones, finish releasing the new versions and then finally get back to work on new features that are harder to develop and will make the project more useful.
There are also several unfinished patches of Oliver which can be useful to the project but require more work to get merged, I think I would like to work on some of those in the near future to merge them (firewall support in netjsonconfig and better support of hardware serial number).
That's why I suggest you to implement this feature on your own and share it too, but without expecting to be merged soon because it doesn't sound like something that should be prioritized right now.
I personally think is now the time to start introducing new features which will have a impact in helping OpenWISP get closer to its goals.
Pull requests that are not urgent can lie unmerged for a while but contributors/users that are interested in them can still merge those in their forks and use them, so the contribution will still be useful in the short term.
Thanks
Federico