Hold your horses

This is a rumor after all. I can't see Apple abandoning FireWire quite yet. Not on the Macbook Pro – after all, it's way too important for quite a huge number of pros:
Music, Photography, Video.
I know, there's thunderbolt. But there's not many devices so far which support thunderbolt (for example digital cameras & audio devices).
It is not primarily Thunderbolt that that is killing off Firewire. It is USB 3.0 also.
Name a new camera that hit the market in the last 2-3 years with Firewire 800 on it? In the consumer/prosumer sprectrum I don't think there are any. You may be able to dig up a handful of niche cameras, but the overall trend with cameras as they have largely converted to "file storage" devices ( they have drives and transfer is a file transfer problem) is to dump FW.
In contrast, the new Nikon D800 has USB 3.0. The first of probably many "pro" DSLR to make that move.
Similar trend on the audio products market. New products introduced over last 2-3 years that are not just warmed over update have increasingly used USB.
Blackmagic rolled out USB 3.0 stuff two years ago and several Thunderbolt devices this year at NAB.
There is a large amount of legacy equipment with Firewire 400 and 800 interfaces, but it peaked several years back. There is huge wave of USB 3.0 products coming. If there are more than one USB 3.0 sockets on these new MBP they are more than aligned with those.
There is a smaller wave of Thunderbolt devices coming also. But it combination of the two waves that FW is loosing ground to.
If anything, they'll include a FW / TB converter. But is it possible to convert ALL the FW functionality to TB?
It isn't really a "converter". There will be a devices with a FW controller in it. That controllers PCI_e interface will be hooked to the TB controller. You will
still be buying a FW controller; it just isn't bundled.
FW in the personal computer context is a "dead ender" technology. It is stuck at 800 and has been passed up on the track. There is "enough" FW features that Apple approximates with Thunderbolt (e.g., 'Target DIsk Mode' ) that FW will just get passed by. There is no need for TB to exactly duplicate FW.
Folks that need a FW controller will just have to buy it separately if want it on a Mac laptop. It isn't like that isn't already the case for FW800 on Windows laptops. There may be a FW400 socket but there was no widespread deployment of FW800. Folks who wanted it have to jump to a ExpressCard solution. Going with Thunderbolt isn't that different.
Apple isn't going to include an optional connector. Doesn't line-up with their 'Green' packaging moves to reduce the number of things in the box that many aren't going to use.
It would not be surprising if Apple comes out with a combo "FW + 1GB Ethernet" , "FW + 1GB Ethernet + HDMI " or "FW + 1GB + Superdrive" Thunderbolt device. If not some 3rd party will. The problem with having dedicated single use dongles for both Ethernet and FW is that the cost is going to be painfully high for those that need a more than one of these.
In short, I think for the common "missing port combinations" if there is large enough market a "one port" TB dongle is probably going to spring up to keep the costs as low as possible.
That's another motivator for the two TB port set up. One port for either a single TB port, bus powered dongle or a legacy Disport Port device. The other TB is free to handle other pure TB chains without having to worry about device placement in the chain. (or worry as much about placement.).
An Ethernet only dongle would be some like a 10GbE one:
http://www.attotech.com/products/category.php?id=15&catid=16
Which is expensive but definitely addresses the "faster than wireless" network speeds when working in a high speed NAS/SAN.