Some might argue that Lenin not so much
created ethnic republics as to
allowed them to be formed. Lenin in fact sought to use the various nationalisms as means to an end, eventual reunification under the Soviet banners, those of the international proletariat. For the small nationalities, independence and freedom from what he termed "Great-Russian oppression" was the intermediate stage towards a true workers' state, a way to unravel the reactionary and imperialist structure of the Russian Empire to build a new organisation from scratch.
It was also a way to garner support from the minority nationalities for his own goals: a wholesale rejection of the rights of, say, the Balts, the Finns and so on would seriously erode his base of support in revolutionary and Civil War conditions. A lot of the early champions of the Bolshevik cause came among the minorities, after all.
Given how logical and possibly beneficial such a policy, at least as a temporary expedient, must have looked like to Lenin (
who did write about the issue at length), I think making him abandon it might require a comparatively early POD. I also think abandoning the rights of the minority nationalities in Russia would hurt Lenin and his comrades in a very real way in their quest for support.