> Siberia was colonized by Russia at around the same time, and using many of the same methods, as the British, French, and Spanish were using in North America. In this case the Indigenous population would be whatever native Siberians were living there before Russian settlers came.

I think in many ways it's much less comparable to the British, French and Spanish colonialization of North America and more like the European expansions within Europe (for example France with Alsace or Spain with the Basque country). The area of the JAO for example was under Chinese control (as part of Manchuria) until the mid-1800s. After that, it came to Imperial Russia, who settled Cossacks from Transbaikalia there to secure the border, ethnic Russians and Ukrainians also moved into the area. But these settlers came in the Imperial Time, long before the JAO was officially established in 1934.

So before the JAO was established, there were Cossacks, Russians, Ukrainians plus some Koreans and Tungusic people - but it was relatively sparsely inhabited. Since the Soviet Union was also afraid of the border being vulnerable, they wanted to settle people there in larger numbers.

At the same time, the big Jewish settlements in the USSR at the time were in Ukraine (before the war, Jews were the largest population group in Odesa, for example) - but there were also pretty frequent pogroms against them and the situation was tense.

So the long-term plan was to have the Jews live in a new Autonomous Oblast (giving them an amount of self-determination, though mostly on paper, thus counteracting Zionism which was a pretty popular ideology among Soviet Jews in the 1920s-30s and simultaneously appeasing tensions with antisemites in other places) and therefore bringing development to the border.

Birobidzhan (the capital) is a relatively young city and was mostly developed under Stalin. In the early years, relatively many Jews came (but again, they were always a minority), but the problem was that Stalin was very antisemitic, so the Jewish political institutions were very often targeted.

As far as I know, the people who were already living in the area were never supposed to leave and in fact, non-Jews also migrated there along with Jews the whole time. Making it Jewish was more of a prestige object, but on the whole, the Soviet Union at the time was quite suspicious of religion, so it's not like it was supposed to be an actually culturally Jewish place in the sense that it was supposed to have Jewish inspired laws or anything.