If I remember correctly, management told that they have no plans to list insurance subsidiaries anytime soon.
Regardless, listing of insurance subsidiaries is unlikely to unlock much value for Bajaj Finserv shareholders as in all probability they will go for IPO instead of demerger, and in that process the shareholding percentage is likely to go down as well.
Lastly, I find the scepticism towards holding discount a bit astonishing. The only disadvantage of holding company is that the discount may broaden in occasions but there are greater chances of the discount remaining the same or narrowing. In the later cases one gains with the growth of the underlying companies.