I think travian should find a way to stop players from deleting accounts by a sort of encouragement for smaller kingdoms in early midgame i don't know how maybe if non united kingdoms could rally their offenses in one wave or smt similar it would keep more players until the end game on it and top kingdom will not rest until the game ends.
The main problem with this is: TK has a more or less positive feed-back loop: the more players there are in a kingdom, the faster that kingdom will grow, thus it invariably creates a sort-of runnaway effect, or to an oligopol. This is true for both, victory points and treasures (of course, one is generated by the latter). The game misses any negative feedback which comes with size like increasing difficulty to earn new treasury slots or dimishing network effect e.g. by reducing robber camp and hideout profitability or adjusting somewhat relative combat power.