The previous Tata Sierra which was discontinued was a 7-seater car but as of now, the brand hasn't revealed any specification of the upcoming electric SUV Tata Sierra. So we would suggest you wait for its launch and stay tuned for further updates.
It would be difficult to give any verdict because so far Tata hasn't stated that the Sierra will come in production or not. If Tata finds the SUV commercially viable, it will be put into production in the near future. So we would suggest you to wait for its official announcement.