I would like to pick up following request in the mailling list, because we have a similiar problem:
We have several different projects on our plattform that are using our Nexus instance as artifact repository for the development. It is not intended to be used for archiving purposes. We periodically have the issue that our backup space for release repositories runs out and we have to ask the projects which artifact versions are obsolete (e.g. they never were released to the customer or they are out of service) and can be removed. We also order new (quite expensive) expansion of our storage, if it's necessary.
With the blobstores that were introduced with Nexus 3 we get the possibility to better organize the used storage of each project. However we still have the problem to monitor the disk space in order to prevent system failures due to missing disk space.
With the feature to restrict the maximum size of blobstores, we would gain the possibility to define capacity quotas for each project and ensure the stability for other projects when one project violates them.