Hello Luis and Michael
I has tried create 200 000 device, vmboxes, callflows in one realm. And encountered some difficulties in such an approach.
They are all somehow related to access to the database or management complexity through webinterface.
As example management issue you can try create device with numbers from 10000 to 19999 and change setting for device 15123. My browser is not able operate with so much json objects.
Any way with same restrictions i has made installation of GEO distributed kazoo cluster with high availability redundancy. Kazoo perfect solution, but has its own peculiarities.
Sergey