The post mentions parallels to the Qing Dynasty, but I want to elaborate on that a little more: whenever an authoritarian system which derives its authority from something other than nationalism (Imperial authority for the Qing, Communist ideology and the Party for the USSR) tries to modernize and liberalize, the danger is that this awakens slumbering nationalism which tears the system apart faster than it can safely adapt.
This is exactly what happened to the Qing: the Chinese population never really liked the Qing, but when it was a mostly hands-off distant authority, they lived with it. But when the Qing attempted to become a modern country with high state capacity, this woke up slumbering Han nationalism which proceeded to tear down the dynasty.
And that's what happened in the USSR too: early Soviet leaders correctly guessed that Russian nationalism had to be suppressed in the Soviet system, or else with the majority of the population and territory, Russia would end up dominating the rest of the country. And to their credit, they mostly made good on this: Russia didn't have too much of an outsized impact on or benefit from the Soviet economy, and representation from other states in the political elite was pretty good. But as soon as Gorbachev opened things up, Russian nationalism asserted itself and wanted to throw off the "unfair treatment", and the USSR immediately fell apart.
There are contemporary examples today, too: I argue this same pattern is what has been happening in Burma. When the junta had total control, they were able to force the patchwork of ethnic groups to mostly get along; as soon as a little democracy got introduced, the Buddhist majority started genociding everyone else.
If you want to open up an autocracy, you have to pay very close attention to whatever forces it has long been suppressing.