What am sharing ia an insight and am sure about the news that Tata were in talks with Cherry fot platform sharing which didn't work out.
I beg to differ here as the all five cars you mentioned were never best in class handlers and the weight of the car result in body roll, low mileage and other issues.
X1 platform was based on X0 and was highly re engineered by India team from the original pininfirana design.
Yes now they have good resources like Dr. Tim leverton and Pratap Bose which can build new generation platforms but will take time.
The challenge that Tata got is that they need AMP more than any other company because they have only India market where the design/model ages pretty fast and Tata reputation fail to sell enough volumes to get the cost recovered for the particular product.
Sir you mentioned about parts sharing - it's always good to share parts however not the way Tata practices it. Use it in wisely manner. Use engines, control stalks, platform suspension, seats, stearing system, ac equipments to name a few but not make them quite identical as what they did with 5 products you mentioned and specially bolt and to an extent Zest.
I have examples- they using the same Harman system in all cars. If they just change the outlook my be some buttons/capacitive touch and it will be termed as new and good for Hexa but Tata is Tata. And guess what it will not cost much money as we can see the same in mobile industry these days. I can name lot of phones with same tech parts inside but totaly different from outside.
What about gear box? Due to gear box limitations they were not able to use the best out of engine capabilities. They scrapped CR4 90 bhp, the revetron engine was actually capable for more power but gear box is not. Common Tata why? From last 5 to 6 years...no development on gear box
Sorry if am sounding devil as I want Tata to succeed and be the top player but Tata need to understand that at this point in time they need to do extra not the have baked efforts.