SPOILER: Thousands of Neo clones!
I picked up the November 2002 issue of FIRST magazine (the only movie magazine in Asia), and there was a four-page feature on the Matrix sequels.
Here i quote from the preview:
"...Silver says one visual effect for a shot in one of the sequels took two-and-a-half years to create, and prepares for production on 'a 14-minute sequence that is the most complicated sequence ever put on film' - an effects-filled sequence in which thousands of Agents Smith battle thousands of Neo clones..."
It's a top-notch mag, so I choose to believe it...
Well there you go, the fight will be mind-bogglingly spectacular!