Nice, idea. :)

But what is a “manifesto pledge”? (I assume you mean these, but I don‘t know whether it‘s clear enough)

Additionally, how to check that? I assume we would argue a lot whether the winner “follows their manifesto pledges”.

Besides, this Rule would be deleted when the next Dynasty starts (if the winner wants to do so). I consider some ways of “This rule may not be deleted”, but that‘s not really trivial.

Finally, I don‘t know whether we haven‘t enough ways to avoid such things. First, why should an Emperor do so? Second, we could all idle out and the Emperor would feel alone, third, the Emperor isn‘t the only person who can lead a Dynasty to specific theme: All other Players have more power than the Emperor.

So: 

Per keba

If the next Emperor took their dynasty in an unannounced and unpopular direction, it’d be easy enough for the players to steer it back themselves.

  Dynasties should be Markov chains: this dynasty affects the next dynasty, but does not (directly) affect the dynasty after that.

Five dynasties? Surely? Note that such restrictions are normally implemented in terms of anonymous dynastic rules, which could, obviously, be repealed by a new emperor. So this is broken as well as a terrible idea.

if only this worked in real life :)

Hard to ban someone for five dynasties, unless the next five emperors all kept this rule on the books.