The fact MNCs have been reserved does not necessarily mean further operators will enter the market. MNCs are often assigend for test networks and also as reserve for existing network operators. In Germany each of the four network operators has 2 or 3 MNCs. Allthough one MNC is enough to assign 10 billion IMSIs, another MNC can be needed, since often large IMSI ranges are reserved for certain services or customers (e.g. for prepaid services or for business or institutional customers).
MNCs are also issued to
TETRA networks, (real) MVNOs and to the military for out-of-area deployments.