My personal opinion.

Ekal Jatiya republic agenda was forwarded by Maoist to secure the support from various caste based groups. It might not seem as one but in the root it follows the principle of Divide and Conquer. Brihad Madhesh, Kirat Rajya etc feed the interest groups which inturn solidify the support for Maoists.

Now Maoists are in power, and possibly will win most of the CAs seats (still not the majority), they have to rethink this strategy, what if the divided group becomes a force in itself? Besides these groups are already a nuisance to the party.

Whatever the reason be, and whoever is preaching it, I hope my country is never divided; certainly not on the basis of caste or race.