1. I'm not planning for this, as it has a runtime cost, but it can easily be done with a plugin[1].
2. I'm not planning to implement filters, as you can use methods instead. Refs might be coming if there is enough demand.
3. Moon is actually going in a different direction from Vue now. The core API will be very similar, but it might not be a drop in replacement for some of the advanced features of Vue. Most directives work, components are similar, but it won't be fully compatible.
[1] https://jsfiddle.net/btoegknn/
EDIT: To answer your edited question: I agree, Evan is a super smart developer, kudos to him for building Vue!
Applying some of the performance improvements might be a little complex for Vue, because Moon's compiler is fundamentally different in a couple ways. It generates code for a stricter HyperScript-like syntax (called "HyperMoon"), while Vue aims to be compatible with JSX as well.
Differences like these, while might seem small, are actually pretty complex when implemented in code.