Multi tenancy is an idea that has become particularly important in SAAS applications and the concept holds true for FM solutions both from the perspective of potentially having multiple "tenants" but also to only revealing certain records to certain users. Currently the only way to do this is via the security model and the implementation as it stands has some deleterious issues associated with it both from a performance and display standpoint. (granted creating an interface that constrains by find is possible but it's a kludge and hard to manage.)
It would be a boon if you could assign a key to a layout or via declared variable that would constrain all actions to the record set based on the key. This would not impose a performance hit and you would never see or interact with records that are outside of the key.
This would allow easy management of group privileges within any solution and open up the possibility to open up multi tenancy as FM develops it's cloud strategy.