Finally, someone who grasps it! I was reading this thread shaking my head. Marches are extremely situational, but can be very useful in those situations. I also tend to like having one vassal in my pocket at all times to run around sieging and destroying the things I might have missed with my larger army. To have that be a specifically military vassal is now a bonus. Like he said, these are not meant for you to annex in the near future, that's just a rare option if the situation massively changes and they are no longer managing your border in 100 years.Marches are specifically to make a military vassal. I don't know where you guys get this idea that they you are supposed to blob these guys up and annex them later. You turn nations with good military ideas into marches: Brandenburg, Poland, Ottomans, moldavia, ryzan, nepal, etc... You get them to 55-60 base tax and that's it. You declare war and they send their troops. With moldavia for example - they start with 10% morale and they get some more military bonus's in their ideas. You feed them some land and they contriubte alot of miltary support.
The reason you can turn them back into vassals is because in 100years things could change. It gives you some options.
With that said, I agree that the 60 basetax rule that removes their march bonuses should also change them to a vassal, since that's essentially the way most marches progressed over time as their border became stable.