BMW is phasing out the N55. If a BMW motor is use than it would more than likely be the B58.
https://en.wikipedia.org/wiki/BMW_B58
http://youwheel.com/home/2016/03/27/detailed-analysis-the-bmw-b58-inline-6-cylinder-engine/
http://www.n54tech.com/forums/showthread.php?p=430180#post430180
Tada San's promised 3 model sports car lineup looks like it might actually come true! The render looks cool but doesn't look accurate to the shape of the test cars IMO. The front hood is too long and flattened.
2018 BMW ‘Z5’ spotted at Nurburgring, interesting aero kit
http://performancedrive.com.au/2018-bmw-z5-spotted-nurburgring-interesting-aero-kit-video-2619/