Landless vassals are a ticking time bomb in general. You can limit landless adventurers, but there are no limits for landless administrative vassals—and now apparently not for nomads either. So the game is completely broken and reliant on crude mods that cull the population just to keep the game engine from collapsing after 200 years of play.
For example, if in 866 you decide to make the Persian Empire administrative, and then later invade it with the Byzantine Empire, you inherit all its mansion vassals—potentially over 300. Strategoi who lose land because a child inherits keep stacking up into a lag pile.
It’s ironic that the administrative government, which could be the best suited for world conquest, suffers severe consequences if it expands its model. A historical, administrative Roman Empire can already cause major slowdowns in a short time.