The point is that they don’t need a 2/3 vote to join another organization, such as LCMC or NALC, while still in the ELCA. The ELCA won’t like it, of course, but I don’t know if they would follow-through with their threat to expel any congregation that does that.
Yes, it would probably be possible to leave without the 2/3, but then there would be a constitutional issue if they would be able to retain their property.