He wouldn't really enjoy it too much if the protestors win. He doesn't need an example of a successful overthrow of a dictator in post-Soviet space. People might get ideas. His whole doctrine is based on the premise that his Benevolent Rule is the best thing that could happen on post-Soviet space and anything else is the road to hell. And he'll try to make it hell for anybody that would try to disprove it - see Ukraine.

Latvia, Lithuania, and Estonia seem to be doing alright?

They never were truly Soviet. They always considered themselves occupied territories and got out at the first chance they had.

Those are still all Russian "buffer" states. Why would he be enjoying unrest on Russian borders?

Because it gives him an opportunity to increase Russia’s sphere of influence (whether by exerting soft power or outright annexation).

He doesn't want to annex Kazakhstan, who needs this trouble? He wants it to be within his sphere of influence, but deal with their own problems by themselves, preferably in a way that doesn't give people of Russia any ideas about freedoms or democracy. So far it worked pretty well, but now something went wrong...

Did you ever consider it might be an attack on his sphere of influence? Putin's not the only bad actor in the world.

Bingo!

And who was getting really friendly with KZ lately? Yes, yes!

The left wing mob (let's face it, HN) blindly hates on Putin. There's probably more to the story (he may be trying to disrupt their oil export deals), but he's definitely concerned about the outcome.

Most of the Soviet states have performed poorly since the breakdown of USSR

https://knoema.com/infographics/aiykgj/30-years-of-reforms-i...