I made a basic version which is generated directly from the game files, and includes all unique units:
(click on the image for a larger version)
- Each column represents one era.
- Dotted lines represent upgrades by ruins.
- Grey lines represent special UU upgrade paths.
- The unit "combat type", listed under the unit name, controls which promotions are available to it.
- Missiles and non-combat units cannot be upgraded and are omitted from the chart for brevity.