Solo options cannot exist where challenging content lays.

This is a simple truth.

IF there is any option to solo an event that is easier then forming a PT guess what? Everyone will solo it. If it scales to how many people you've brought to the fight? Guess what. People will exclude others so the fight is easier with lesser people. A Tank and a healer and a DD you're good to go. Why add more people to the PT if it is just going to increase the chance of wiping?

Casuilzation is a disease. A poison that will eck into and ruin any hope of having a satisfying Story. There isn't a way you can implement it so the difficulty of a full fledged PT instance can scale to a single person. Either the game is hard and rewards or simple and forgettable. Thems the truths.