(Sorry if this has been discussed, I don't read 360 sections really anymore)
*These are rumours only, no official MS statement has been found*
Numerous sources are indcicating that Core & Premium 360 consoles will be getting HDMI ports in late August - September.
G4 - The Feed - All Xbox 360s To Have HDMI Ports?
Rumor: All Xbox 360 models will include HDMI - Joystiq
Microsoft officially adds HDMI to Xbox 360 Premium - Engadget
That last link contains an "official" Microsoft statement but I didn't find the actual source of that statement anywhere. Its either a one on one with Microsoft they had, or just total crap.
Also note that some sources are saying it for Premium only, some are saying it's for Core aswell.
If all goes as planned and rumours are true, it will cause some selling problems for the Elite over here since its not out yet for another month. The only difference would be the color and the stuipdly humongous HDD.
The HDMI is said to be added with the new chips and a nice HDMI logo will be planted on the box of those colsoles with the port.
Again, there is no real confirmation except from what is said to be an official statement from MS on the last link.