It could, don't the Mac Mini have HDMI?
HDMI makes sense to the Mac Mini at their price point in these times... as they want people to adopt to the OS more than anything with the low price point.
If they didn't have a Mac Mini with a HDMI port they would lose in the market because of compatibly with the screens out their now in the market all utilizing the HDMI port. That's what happened to this - 2009 -
http://support.apple.com/kb/HT3478
I think Apple has realized their mini DVI/display/VGA ports has hurt them in some sense, because the 2nd piece to the puzzle, the LCD screen, which now pretty much have HDMI ports in all sizes has become so relatively affordable. Adding a HDMI was a hard-headed decision for Apple to make in the last update, but it's a smart one for the price point of the mini, and more or less to gain that audience to their OS nonetheless at the cheapest price point. They were holding out, but for the iMac - I think they will indeed holdout for sometime, or until the MacBook lineups receive a HDMI coincidentally... which may be never actually happen the way Apple works/thinks.
If they release a new iMac, then I don't see why not. Apple used HDMI on Mac mini and their latest laptop...
I don't believe Apple will put in a HDMI port because of strategic business decisions of how they get you to sync/port an iMac with a Mac(conceptually, a laptop in any case) or another screen using their proprietary connectors.
Basically, I think the MacBook line would get a HDMI before the iMacs will... does that make sense? If you want an iMac with 2 screens, they want you purchasing another Apple LCD display/screen(WITHOUT HDMI) more than anything else.
This is all my opinion, but I will tell you, this is how Apple thinks, to please all audiences, and to give themselves a better business stance in the markets they want to be in. For some, Apple just doesn't work(whether it be business, aesthetics, not wanting to change from Windows, etc, etc), but for others(many of us on MacRumors)... Apple fits their needs/wants/style perfectly, and Apple gears themselves for this. A lot of the reasons why they never overstock anything!
Apple is better off without the HDMI in a business sense for the iMac... we the consumer are not, but Apple is making everything still work to their advantage, and gaining in most markets. Although, the desktop market is not their highest priorities these days nor most companies in the same field, but they are still making strides percentage-wise.