A Facebook site called Tamil Film Updates posted this folder of promotional images for Shankar's "Robo", with the following description:
Years back, Shankar started "Robo" with Kamal Haasan & Preity Zinta to play the roles of Rajjinikanth & Aishwarya in the present Enthiran. But the project didn't take off at that time due to some issues. These are the exclusive pics from the photoshoot.
This was in 1998. I imagine the film would not have been half as epic as special effects, Shankar's greatest love next to a good social message, weren't exactly fully developed in the late 1990s, but I would've enjoyed this pairing, if nothing else, in these roles. In my Enthiran review I didn't give very high marks to anybody in this film for acting, including Rajnikanth. Aishwarya's lack of acting could largely be blamed on the abysmal writing for the character. Regardless, it's an interesting "what might have been"..
I recommend you check out the rest of the album, if nothing else than for the late 90's sci-fi get-ups.