This solution is not practical when you have more than 200 VLANs and have virtual machines within the network which are not online all the time.
There needs to be some mechanism where the server assigns a role of unmanaged computer to a system in a VLAN on its own. If the unmanaged detector goes down or not available on continuous basis then the server should automatically assign the unmanaged detector role to any other machine within the same VLAN, This unmanaged detector role can also be assigned in rotation between different systems in VLAN based on how idle they are.
Can we think of implementing such option? I will also put this as an idea.