I really can't say much about the culture idea; it just fails to grasp any interest on my part, at least until you elaborate on what do you mean by "culture" and on what the hell is a "culture" player supposed to do with it (as well as how will you prevent excessive interaction between culture and state players). Rome is a more interesting idea, and you might want to ask the Strategos for information if you intend to incorporate religion (let's not call it the way more ambiguous and many-sided "culture" here) there, as he already wrote an alternate history about Late Roman Christian policies.
Now, as to this:
d- Do a standard style NES with the main change being that players play individual rulers, not nations. This means that upon the ruler's death, they actually can't continue with the old nation. This would more realistically stimulate differing policies.
It occurs to me that, while the standard NES system overestimates political continuity, your system underestimates it, badly. While the deaths of rulers do indeed cause a certain political shake-up, it does not necessarily lead to a complete change of policies. In fact, the cases I can remember off-hand of actually radical changes in policy that can't have happened under the same ruler (or, rather, the same
player) were always more like exceptions than rules. Now, if we were talking about
dynasties, this would make much more sense and would be much easier to handle. Maybe you could even merge it with the individual idea,
sort of: have people play different factions within a limited amount of states, with one faction reigning (usually) and others either supporting it or conspiring against it (or both, ofcourse, and there should plenty of space for reason). This would make a ruler's popularity a much more important issue and make suicidal policies (like endless wars or disregard for traditions) less likely.
(Also, as an additional idea, you might want to fast-forward it towards some basic empires with a well-formed monarchic system)