2024 is a fair way off.. Remember, the bigger customers are going to ask for tenders based on their own wish list. Those switched on will be looking for feature and functionality matches. The cloud is about pricing, only paying for what you use. The issue with hosted services, is the security and integrity and availability. On premise is essential for certain businesses, like emergence services call centres, hospitals and federal solutions. Reduced capex doesn't increase reliability or prevent vulnerabilities.
And as the bigger players change out their CS1000 solutions, the market place is going to be flooded with second user spares the smaller businesses can grab to maintain their solutions. The only thing in the market that will cause ANY grief for the TDM world, is if all service providers kill off traditional trunks,(analog, PRI BRI) and deliver only SIP via Fibre to premis.
But Hey.. when the lights go off at the fire station, that old copper analog line from the local exchange will get connected to the POTS set via the PFTU and service will be available.. The CLOUD has no answer to that simplicity of survivability..