It's pretty sure that next year (with the facelift) the S and later the GTS will get a flat 6 (NA).
Several dealers in germany already have that info and gave it to customers.
Also Andreas Preuninger hinted that more or less obvious in one of this interviews about the new GT4.
This engine ist not only for the Spyder/GT4 you will see it also in other models of the 718 range.
There it will have less power. But there will be also a version with more power than in the GT4!
The 2L F4 will stay in the base model.
They get to much complains all over the world about that 2.5L engine. Objectivliy a good engine, but ist lucks the emotions Porsche customers want you get, especially for a price near 100k for an optioned GTS.
I expect the internal number will stay at 982.
No new names like 718/6.
They will stay with S / GTS.
I will believe it when I see it in the flesh. Every corporate indication is that the flat-4s will continue to be used until the next-gen Boxster/Cayman arrives in 2-3 years -- if it even ever arrives at all, since there's still doubt about that. A 'facelift' almost never comes with new powerplants no matter the make, since, well, that implies more than a 'facelift'.
The entire reason the GT4 and Spyder have NA flat-6 engines is because they both are, fundamentally, track-oriented vehicles that benefit from high-revving powerplants. The 718 base/S/GTS aren't meant primarily as track vehicles.
And I believe you should read some recent reviews of the S/GTS. Virtually no one professional complains about the engine's sound anymore. Why? Because the cars are so good in every other way, there's no point in it except to niggle. For a public road-going sports car, the base/S/GTS would be
hurt by an NA flat-6, not helped. The only conceivable way this could happen is if the new 911 were almost exclusively a hybridized/EV vehicle. Otherwise, there's too much market crossover for Porsche's internal tastes.
I could give several other reasons why such a switch wouldn't make sense for the 718. I really don't care what dealers in Germany or Mr. Preuninger have said. Porsche isn't stupid. And sound isn't everything.