Although BlackberryOS 4.0 is probably going to be ready soon enough, they may delay it if the carriers drag their feet in releasing the newer version of BWC (and/or BES). The newer servers are necessary to enable the extra features of the web browser.
I am running 4.0.0.100 and even JavaScript doesn't work because neither the BWC/BES infrastructure is upgraded yet to accomodate the new features. I'm looking forward to it!
Unfortunately, I don't think some carriers will get the 4.0 infrastructure deployed till early next year. Rogers (The carrier of the users at RIM's offices/factory) will be one of the quicker ones to roll it out but even they can lag a bit.
It is possible the first people to have a fully functioning 4.0 browser will be the BES/MDS users, especially if Mailstreet or another BES/MDS hosting service (such as
MyBlackberry.us) deploys 4.0 servers before any of the carriers do.