In ordinary strategies you already have an assumption of immediate information transfer from unit to player - you see what each unit is seeing. This can be kept so you will see you units moving in real time but as things get further from your units on the map, the older info about them you get.

That's interesting. Wouldn't it lead to paradoxes where enemy units are shown at multiple places at once, observed from different frames of reference? Would be incredibly confusing, but confusing games can be fun too.

EDIT: Also if a unit traveled close to C away from a friendly unit, and then back, whos reference is real?

Observations merging is interesting question. Simplest thing to do may be to show enemy unit as it is seen by our unit closest to them (here we just use "real" distance in internal game's coordinates). In other words, Voronoi diagram is built with our units as seeds, and enemies are shown as seen from their cell center. This would evade enemy "phantoms" but enemies can suddenly "teleport" as they move closer to other friendly unit (or can't they? I don't really know).

In lore it may be explained like "our units know distances to objects and choose closest one among all units" since we already use "units can communicate instantly" magic.

You’d have to have a HQ relative to which all dilation is calculated. If done correctly, it could simplify server operations since the need for simultaneity is relaxed.

Would be great as an artistic project, maybe not as a game.

Also in time I bet some players would find ways to win reliably, creating a new field of military strategy.