Actually the new requirements only apply to an ATP with a multi-engine rating. When you read the rules they say to take the knowledge test for an ATP with an airplane category ME class rating you have to complete the training program. Will there be a separate SE and ME ATP test? Will you have to declare your goal when you take the written. We'll know in 7 weeks.
135 requires an ATP to be PIC of a jet with more than 10 pax seats. Some 91 operators require it for an insurance break.
Spend a weekend with Sheppard and just do it.