As a fun little thought exercise, note that Singtel owns Optus, the Australian telecommunications company. So much so that Singtel (the multi-faceted corporation) is much more Australian than Singaporean in terms of its revenues and real business activities. In this SIMBA-M1 corporate transaction Keppel is selling its large controlling interest in M1 (the telecommunications part, not quite all of M1) to Tuas, SIMBA's parent company. Tuas happens to be...an Australian company! Funny how that works.
Hypothetically the government could block this transaction; it has that power. But then the Australian government might get upset and (in extremis) retaliate: the Australian government could require Singtel to divest Optus. Which wouldn't be a great outcome for anyone, would it?
Therefore I think what'll end up happening is that mobile spectrum will be reallocated, and we'll end up with 3 MNOs. We already have 3 MNOs on 5G since StarHub and M1 have a joint 5G venture. A Singtel/SIMBA-M1/StarHub constellation of MNOs would shrink 4G to 3 MNOs but maintain the MNO count on 5G. That seems tolerable to me, but we'll see what the government thinks.
I suppose the government could explore (again) whether there's room for a 4th MNO, another SIMBA basically. But that might have to be a long-term project.