I haven't really considered whether the project will be commercial or open source as I'm not sure if the idea is even practical yet. At the moment, I'm aiming to create a prototype or proof of concept.
As for the features I'm looking for, well that would basically be everything from Daggerfall plus the following:-
- 1st/3rd person perspective
- 3D models instead of sprites
- Sloping rivers and streams
- Reasonably intelligent AI
- Scripting system
- Multiplayer support (up to around 8 players)
- AI controlled player characters (if a player gets disconnected or otherwise cannot play)
- Destructible environment support
I haven't looked at the source for Daggerfall Unity, as it's my understanding that much of Daggerfall's content was in a non-standard format. The same is true of Morrowind, if slightly less so.
When I said the game will be a spiritual successor to Daggerfall, I meant that it would have similar aspirations, rather than be set in the same game world.