What would you like to have changed or added to Vampirism

Bat mode with some adjustments can be quite fun and balanced, an option to prevent sprinting would go a long way in making the flight less overpowered.

Does this make the mod experience more balanced?

Yes.

Can you provide additional resources (etc. textures or models)

N.A.

This would require some ugly code I think.
What do you think about an option to modify the base speed in bat mode. E.g. to a level where the sprint speed is as fast as the normal non-sprinting flight

The ability to change how fast the bat can move would help immensely, and would be a fine alternative to hacking away the sprint option.