As someone that sherpas, I've spent countless hours on an idea like this. I just don't have the technical expertise to make this a reality. It could be presented as a "simulation" where new players can be exposed to the raid in a tutorial-like setting. Each encounter is broken into small, digestible roles to allow for easy understanding. Players can launch into any portion of the raid at their leisure to focus on specific roles/encounters that give them trouble. Most sherpees I've encountered aren't fearful of the actual raid, mechanics and/or difficulty. What generates anxiety is the feeling of letting someone down and/or wasting people's time. If there was an option to allow players to learn the raid at their pace, I truly believe that the raiding population would flourish in numbers and open up a whole new demographic to raiding.