This question a follower was wondering about!
I don't think that the advanced social dancers have all techniques at top level and if the leader wants to lift up something the problems can be similar to those at my level. When I want to add a variation of a known figure to my milonga vocabulary there are just a short rough period and then we can catch up the normal flow. If I instead want to introduce, develop a for me totally new technique the situation is quite different.
The day I want to expand to a new skill I start to work on it at home up to a level I remember the steps for me and the follower on the chosen figures. After that I can have a private lesson with a teacher but later on I need to train them with a partner and Yes! At this point the problems start!
In my world most of the followers start at beginner courses but as soon as they can atract sufficient number of tandas most of them stop regular courses and trust on that the leaders will teach the rest of the needed skills. There are not many at a practica who wants to sparring dance with me not even if I promise to dance the same number of songs so they can train the steps of their choice!
When it is time to introduce the new elements to an informal milonga there is a clear drop of skill on several areas. Even if I can move ok on pista the flow is not so smooth, not so effortless. When I am tweeking in the new steps the variation of other content gets lower as well as my focusing, selfconfidence and musicality.
There are followers who do not accept this drop in the tanda quality, but want a full dance experience always! This forces the leader to seach new partners and here is an opportunity for the followers willing to cooperate in learning and learn themselves. Maybe you are interested to get new friends also! Here the changes are quite obvious!