The first iteration of Nissan's ZX-Turbo IMSA prototype will be introduced to Forza Motorsport 7 in April 2018.
As stated in the most recent 'Week In Review' post on the official Forza Motorsport 7 website (since updated to remove the Nissan reference), the 1985 Nissan ZX-Turbo – which isn't currently available in the game – will be the featured car in the upcoming "April Car Pack Challenge" Rivals leaderboard event.
The Rivals mode theme confirmation also reveals the Nissan GTP ZX-Turbo will be featured in Forza Motorsport 7's April Car Pack. No other details on the DLC are known at time of writing, though it's expected the Car Pack will be released in conjcuntion with Forza Motorsport 7's next content update on 10th April 2018.
It was confirmed, though, that more information on Forza Motorsport 7's upcoming April update and DLC will be revealed closer to their respective release dates.
The 1985 Nissan GTP ZX-Turbo was the first of the many prototype racing cars fielded by Nissan in the IMSA GT series. Built on Lola's T810 chassis, and fielded with factory support by Electramotive Engineering, the original Nissan GTP ZX-Turbo was never able to challenge for title honours in 1985. However, the lessons learned in the car's development helped pave the way for Nissan's eventual IMSA dominance in the late 1980s and early 1990s.