Space stretching can be represented by a closed
universe where there is no boundary expanding at
the speed of light. Instead the space inbetween
the galaxies is stretching.

To answer my question, the space stretch can be
represented in Riemanian geometry as the expanding
surface of a hypersphere. Curvature would go down
inbetween the galaxies as more distance is created.
Gravity will only get weaker inbetween galaxies.