Ok, having abandoned my previous timelime featuring the survival of the Byzantines, I am in the process of cooking up a new TL, which will have a more Medieval plus Renaissance feeling to it (well, at least in its beginning).
This timeline involves an X-Lithuanian Commonwealth, where X stands for a yet undisclosed country (hint: it's not "Polish" and it's not "Muscovite"). Basically Jogaila, instead of marrying Jadwiga of Poland, marries someone else. However, this new appearance on the scene of history will go through mostly the same processes as Poland and Lithuania so it will eventually face the same problems.
So for my purposes let's do a case study of the late 17th century breakdown of the Polish-Lithuanian economy, society and political institutions.
The AHC is thus to fix the problems of OTL's Polish-Lithuanian Commonwealth in the later half of the 17th century. It will be my job afterwards to apply those same processes that cured the PLC in this challange to my timeline's different commonwealth.
My goals are:
1) To avoid the further stratification among nobility. Of course that is kind of tricky, and eventually the magnates will grow in power and wealth but at least I'm wondering what could be done to keep the middle and lesser szlachta in control of the General Sejm and especially of the local sejmiks despite the magnate's increase in power and wealth.
2) If possible to almost entirely avoid the disintegration of towns and urban classes.
3) To keep and further education (especially among middle and lesser szlachta) and avoid the cultural decline.
You can assume the PLC to be much more successful and powerful in relation to Muscovy than it actually were. [That is because my alternate-commonwealth will be much more powrful in relationship to Muscovy due to other factors. However, even in my alternate-commonwealth the Khmelnytsky thing still happens, but in my ATL it will be a nation-engulfing civil war and Khmelnytsky himself will be a Cromwell-type figure, he won't have the goal of an independent Ukraine, mostly due to different demografies from OTL. So while my question relates to OTL's Polish-Lith. C. and not to my ATL, take that into consideration, you can assume there will be no territory lost, but there will be nation-engulfing war, even in the potential absence of the Deluge.]
Ok bonus points if you have the Commonwealth involved in wars and still able to recover and reach the 3 objectives stated above.
Also, notwithstanding the devastating wars, there were apparently other causes to the economic collapse in the Commonwealth, causes affecting the entire continent at that point. So extra bonus points if you can give an economic solution at least as good as other countries'.