The choice of resolution is partly because 1440p up-scaled to 4K looks markedly better than 1080p, and partly for the general buying public 1440 is a higher number than 1080.
I guess depends on scaling methods - I had read before that 1080p much better to upscale to 4k as directly aligns than 1440p which is more complex ?
Presumably the Series S would output at 4k/60 but rendered at 1440p internally ? Quite a lot of work for it to do ?