That post is old and therefore not updated.
interoperability has been implemented by SEBI Circular since july-2019 and clearing Corps of both exchanges can set-off trades in the other one. ( Like what brokers did yesterday )
The issue is that the Trading/Broker terminals not yet fully ready as every brokers terminal has to support it. When all are ready, you will be able to buy and sell intraday across both exchanges. ( if they work towards it )
But then this will mean that price spreads will become very small b/w the two exchanges and maybe those Arbitrage guys will have to find a new strategy
On the other hand, it is good for BSE as its volumes will improve( plus earnings ) & maybe that is why NSE isn't very happy about it.
Ofc, the same scrip should be trading on both Exch.