It may even be called the i9 and will come with a more powerful 430 hp+ drivetrain.
Speculating on upcoming models is by definition an imprecise art, the rapid pace of technological development muddies the waters even further which is why most manufacturers tend not to get too specific about future models. Yet a lot of information can be gleaned from what they are up to behind the scenes, take BMW for instance, BMW Blog claims that while the i3 won't be replaced, an i8 replacement is still on the cards and it may well feature a more powerful four-cylinder engine in place of the current three-cylinder unit.
This rumor has made the rounds before back in 2015 when BMW was still toying with the idea of a higher performance i8S variant. That model never happened but BMW Blog's sources say that there is no reason why BMW couldn't replace the current 228hp turbocharged three potter with a 300 hp four-cylinder engine in a new model. The current car produces a combined 362 hp so we can expect at least 430 hp from the new combination.
BMW's commitment to adding 25 electrified vehicles to its range by 2025, of which 12 will be fully electric, may mean that the longer the i8 replacement takes the more likely it could end up being a purely electric sports car. Piecing together factoids about this possible new model such as BMW's recent renewal of the i9 trademark could well be pointing in this direction. Whatever happens, the current model has only recently been refreshed and a roadster model added so a replacement of any kind should not be on the cards until after 2020.