Perhaps the next x-box will use it but not Nintendo, Nintendo always use a different format (or at least they have for three generations running).

you got to think in the future. they're already testing new disc that holds 3x as much space a blu-ray can store.

possible but there are many possibilities.

Sony will definitely use Blu-Ray
MS could easily use HD DVDs as their main media, but they might use Blu-rays as well.
If Wii 2 is as technically inferior (I hope people don't jump on me for saying that) as the Wii this gen compared to the other consoles, DVD9s could be enough.

the question is why would they use them ?

They're much more expensive and the games are not nearly as big as these discs.

and I doubt Ultra HD will be the standard for next gen...

Sony will definitely use Blu-ray on their next console, no doubt. Nintendo is expected a HD console next and they need to put a large amount of data their. HD-DVD is dead and normal DVD holds only 9 gb. So, I believe Nintendo will use Blu-ray as well.

Microsoft may stay on DVD and try to release a console with low price without paying for blu-ray (which seemed to be working this gen), or they can use download only as their main target is Europe and USA where many people have high speed internet.

Blu ray players are getting cheaper now and soon no one is going to buy an DVD player and all have Blu ray like VCR to DVD players. Blu ray will last another 10 years before any new disk format is introduced. 

MS going DD has to gamble if an Internet revolution occurs in the next 5 years or else the next box is an failbox 

None of them will be download-only. The trend is of course going that way, but the time's not ready yet (hello PSP Go) and it won't be for at least 5 more years.

Disc-based media will again be the only option for all next-gen consoles, so all of them are going to use one of these:

DVD

HD-DVD

Blu-Ray

Sony is of course going to stick to Blu-Ray. Piracy-wise, HD-DVD would be an interesting option for Nintendo and Microsoft, but I'm quite sure neither of them is going to use it. HD-DVD is dead, so using HD-DVD would be very expensive because nobody produces the technology anymore. By the time the consoles launch, Blu-Ray technology will not only be superior, but much cheaper than HD-DVD as well. And customers of course love Blu-Ray - to sum it up, HD-DVD is not going to come.

So in the end, Microsoft and Nintendo will choose between DVD and Blu-Ray. Lower production costs will be a small advantage for DVD, so Nintendo might eventually stick with DVDs. Microsoft however will most definitely pick Blu-Ray. Consoles have turned into media-centers this generation already, and the customers like it. With next generation consoles using Full HD, 3D graphics etc., a console/media center that only supports low definition video DVDs would really seem oudated

No only the PS4 will use it

Isn't there a chinese version of HD-dvd that is in wide use?

When next gen begins, BD will be dirt cheap, and whatever game needing more than one DVD will be cheaper to put on a single BD. Most probably Ninty will use the BD HW base and physical disc, but with a proprietary data format, to pay almost no royalties to BD consortium.

About royalties, both BD and HD-DVD use the same two main video formats, one of which was developed by MS that released it for free, but still owns one of the most used codecs for it, so MS too indirectly gathers a small chunk of royalties from BD. MS pushed HD-DVD before its death because it owned the most used implementation (*) of its interactive contents and because despite not being overwhelming, Sony is one of the biggest members of BD consortium, and finally also because BD interactive contents are based on a Java derivative, that MS hates, besides not earning a cent from it. Now that HD-DVD is dead, MS can bite the bullet and accept BD, it will gather its small chunk of royalties, smaller than what it could get from HD-DVD, but better than nothing, and enjoy economies of scale, as many correctly pointed out, and the convenience of the bigger space available, and it will gather a small satisfaction too, that Sony bore most of the financial efforts to launch BD and bring it down to mass market affordability, also losing consoles leadership due to the excessive price it initially forced PS3 to have.

(*) (based on  WinCE, IIRC)