Just because it isn't officially revealed doesn't mean that software support can't be announced before it's reveal much like how Ubisoft, Square Enix, and Sega have already declared support with games prior to NX's unveiling ... 

We also don't know if it's Tegra X1 or X2 is housed in the NX since those are just rumors. Even if it's using Tegra chipset and is getting engine support there's no guarantee that you'll end up with a similar technical experience either ... 

No it doesn't mean, but it also doesn't mean they need to announce software support before revile of console, espacily beacuse Nintendo itself still didn't tell anything about NX expect March like release date, not any other single info.

Tegra X1/X2 is heavily rumoured from multiple different reliable sources, so even that is still just a rumour we can say that is most likely true. Experience depends from power of hardware, engine support is something totally different, Tegra X1/X2 supports UE4 than console that have them can run games with UE4.

What Epic Games needs to do is support the API, not a specific chipset ... 

The latest UE4 (ver. 4.13) still hasn't got support for NX as of September 1st! Yes, the experience depends on the power of the hardware but engines have a min spec and you should be worried about the the implications of that since it could imply that the NX is still too weak to power UE4 ... 

And how that have with fact that NX is not listed like suporter?

NX relly doesnt need to be listed like UE4 suporter at this point, like I wrote, "it doesn't mean they need to announce software support before revile of console, especially because Nintendo itself still didn't tell anything about NX expect March like release date, not any other single info". Also like I wrote, Tegra X1 is strong enuf to run UE4, and NX will most likly have Tegra X1 or X2, and we also have rumours that NX is definatly suporting UE4.