Sounds pretty cool!

Since you're pretty much at design stage, two ideas are worth exploring:

1. Uniqueness typing (re: linear typing for mutable data) is a neat addition. The paper by John van Groningen et al seems the most appropriate: "Exchanging Sources Between Clean and Haskell: A Double-Edged Front End for the Clean Compiler."

2. The Shen lanaguage http://shenlanguage.org/

Clearly, these may not map directly to the features in the final design, but the ideas they cross-pollinate will be very useful.