Actually, it's very likely that Sparrow does already support that new resolution!
If the rumors are true, we'll simply get a new scale mode. Sparrow will recognize that mode (3x) automatically and will look for "@3x" textures. If it doesn't find any, it will use the "@2x" ones. TrueType text, on the other hand, will automatically be rendered in the new resolution, as well as Core Graphic vector textures.
This is even true for Sparrow 1.x, BTW!