The Soviet Union seems like it fell into an awkward position in its ethnographic balance, the ~50% range of the main ethnic group, since it was too Russian dominated to be viewed as really pluralistic and multi-national, and yet not so much so that like China, the main ethnic population absolutely dwarfs to irrelevancy the outlying minority populations. Although the 1920s saw significant experiments with korenisizatsiia, ie. indigenization, this was shortlived and by the 1930s the policies of Russification were once again full swing, and it's telling that the shorthand name for the USSR abroad was most often Russia. Although this worked as long as the system was stable, when it became unstable, resistance against Russian domination flared up which the Russian population was not large enough to render irrelevant as happens in say, Han-dominated China.
But what if the percentage of Russians in the USSR was substantially lower? Let's say that in the 1919-1920 period the Soviets, as they very might have done, manage to win their wars in Finland, Estonia, Latvia, Lithuania, and Poland - and not only this but particularly in the first four, mostly due to the actions of the local communists of those ethnicities, such as the Latvian Riflemen and the Finnish Reds. These are ultimately joined into the future USSR as SSRs, and perhaps the process repeats if future territory is added on. Would a much larger, and more authentically national (as opposed as simply being installed by foreign bayonets, with the admittedly glaring exception of Poland), selection of SSRs be enough to shift the ethnic balance in the USSR enough that it would cease to simply be greater Russia with red paint?
But what if the percentage of Russians in the USSR was substantially lower? Let's say that in the 1919-1920 period the Soviets, as they very might have done, manage to win their wars in Finland, Estonia, Latvia, Lithuania, and Poland - and not only this but particularly in the first four, mostly due to the actions of the local communists of those ethnicities, such as the Latvian Riflemen and the Finnish Reds. These are ultimately joined into the future USSR as SSRs, and perhaps the process repeats if future territory is added on. Would a much larger, and more authentically national (as opposed as simply being installed by foreign bayonets, with the admittedly glaring exception of Poland), selection of SSRs be enough to shift the ethnic balance in the USSR enough that it would cease to simply be greater Russia with red paint?