I doubt many nnew players are awaiting to be a slave of another nation tbh. And you also have the lack of diplomacy on the other side. In order for this feature to be used both the offender and the defender need to be diplomatically skilled. Which makes effective use of such a feature still void. You wish to add another layer but as stated above.
Andd maybe if people would start actually using diplomacy instead of jumping into coalitions never saying a word...
Most people aren't using current diplomacy not to make alliances/coalitions not to trade not to talk strategy. Both on winning and losing side. Why would somebody who just destroyed another nation spare him so that person can backstab later? Most winners wont do that.
And most loser would leave before you can even message them. My conclusion remains
Then I'd rather have bytro focus on other features that aid both the RP and the Regular community. Andd maybe if people would start actually using diplomacy instead of jumping into coalitions never saying a word... Then Maybe this idea becomes valuable else I think still 95-99% of the losing nations will leave, especially taken that most people already leave if they lost their main army even way before the enemy enters their territory