I agree. This is a slippery slope and opens a whole can of worms. What's there to stop a person from serving 20 years, 30 years, or even for life. This is actually a catalyst for instability, not vice versa.
What is wrong with someone ruling for 20, 30, 40 years or life if he is an excellent leader with high morals who genuinely wants nothing but to see his country be the best? This is a country that allies can trust and enter into long-term commitments with. Would you prefer he be replaced with a different idiot every 2 years who needs to leave just as he's getting the hang of things? That's true instability; countries don't even dare enter into long-term deals with you because they're afraid that 18 months later the next guy will cancel it.
Don't interpret what I said to mean that I think leaders should normally govern for life. I mean that there needs to be a mechanism to differentiate between great leaders and poor ones, reducing the term of the poor ones and extending the term of excellent ones as long as they continue to be excellent. That is an ideal system that no country in the world has achieved but China creating a merit-based term limit could be in the right step
if it is implemented properly. I can't speak for the future and who
might be able to abuse this down the road if the specifics aren't well-designed (and neither can anyone else), but as things stand now, Xi deserves more time to bring more greatness to China.
If they're unable to work out such a complex merit-based term limit system out for now, they might just extend the max term to 3 or even 4, which would simply represent a different risk vs benefit strategy for China, tilting more towards giving power to excellent premiers to enact long-term strategies while detracting from automatically limiting the corruption of poor premiers. If they do this, at least they come out of the gate winning with Xi. After that, might be better, might be worse than the current 2 term limit; don't know.