So eeconf 2025 - complex layouts talk notes that the docs don't make it clear you can use a layout variable as the template_group/template value when setting the parameter in the top layout tag.  This really opens up some options to conditionally determine what layout to use in earlier templates.
So- note that and it would be nice to include an example of how/why you might do this.
Also worth noting somewhere how well it interacts with caching.  Template caching doesnt help- tag caching may well be worth it.  Speedy fragment fcaching can be applied to end.