My personal starting point for thinking about [imagine] is Ron Edwards' work - what you call [imagine] he calls [exploration].
He identified five elements of it, in RPGing:
*Setting (your [world-imagine])
*Character
*Situation - this is the immediate motivating circumstance in which the character(s) find(s) themselves
*Colour - atmosphere, tropes, "mere flavour", and the like
*System - how the content of [imagine] changes - system is what puts the game into motion
Vincent Baker's analytical work in relation to
system is (as you know) extensive, and in my view powerful. Your third and fourth dot points (
norms and
mechanics) pertain to system.
Your first two dot points seem to me like articulations of (what is in my view) the key idea that the principal limit on a player's moves (via declaring actions for their characters) is
what everyone is prepared to imagine together (which is, of course, informed by
system).
I think the relationships of
character => situation and
setting <=> situation are very interesting. These relationship differ in different RPGs, and are key sites of differences of system.