AFAIK, the 65nm processor is definitely meant to be true. I'm sure MS announced something about that last year.
As for the rest.....
Bigger HDD -
Hell, why not? The original 20GB HDD is pathetically small (the HDD in my original XBox is bigger

), especially with MS now pushing TV & movie downloads via XBL (in the US, at least, dunno when they're due here).
HDDs are cheap, & MS are now starting to make a profit on 360s AFAIK. They could stick a bigger HDD on, maybe charge a little more, & still make money. And they'd then beat the PS3 for HDD space (twice the size, lol, if this is true).
They could also sell the bigger HDDs separately, just like they do now with the tiny 20GB ones, so those of us with the "original" 360 can upgrade [as long as they don't charge a rip-off price]. Only issue with that is what do you do with all your saves & DLC & so on? Memory card to transfer, or some other method?
Built-in HD-DVD:
Doubt it. It'd push the price up too much, & they won't want to be fully locked into one format over another while the current HD disc format war is raging.
HDMI:
Maybe, if the rumours of the "original" 360 being unable to output digital AV are true (hence the lack of an HDMI or DVI cable after over a year).
But, MS have said though, when asked whether they would provide HDMI, that they would do so if the need/demand was there.
So hopefully they will find a way of doing an HDMI cable, rather than only having HDMI available for 360 mk2.
If the 360 is incapable of having an HDMI lead, then anyone with the HD-DVD drive would be utterly screwed once the movie studios eventually start releasing HD-DVDs with the Image Constraint Token (ICT) enabled - with ICT on, HD resolutions are only possible using HDMI (or DVI with HDCP), if analogue connections (e.g. Component) are used, then your fancy HD-DVD movie gets downscaled to 540.
The photo does look a bit crap though, & wasn't there a similar rumour recently which turned out to be fake?