This is the smartest BJP move.
This is what I think has happened.
BJP knowing that it can’t form Government is taking steps keeping its eye on the future, not on the present.
BJP wants ShivSena to form a government with NCP-Congress help. BJP will then not only dissociate permanently from the ShivSena, but will declare ShivSena as an anti-Hindutva party. It will then declare that it is the sole Hindutva-nationalist party in India.
As a consequence, it will remove ShivSena ministers from the central Cabinet, where BJP has sufficient numbers.
It will then aggressively try to persuade the ShivSena’s hindutva voter base to switch local ties and join BJP. It will also expose ShivSena as being unprincipled and power hungry.
At the next election, which may well be midterm, using the party’s power at the centre, BJP hopes to improve its strength sufficiently to not only win Maharashtra back with absolute majority, but having increased its credibility as the only Hindutva nationalist party. It will then have destroyed ShivSena completely in Maharashtra and firmly caused the Hindu loyalists to permanently switch loyalties.
This will be their long term game.