I doubt there will be any mergers any time soon. Too much pressure to reregulate the railroads. BNSF in particular has too many people mad at them (the state of Montana for one) for them to get very far with a merger in the current governmental climat. Many in congress (at the request of shippers and rail labor groups) are currently researching how far railroads should be reregulated. Latest locomotive emission standards are going to be a big hit as it will apply to any locomotive overhauled (according to the AP wire story printed in many papers) as well as new locomotives. Short lines will have a difficult time footing that bill.
I predict railroads will start getting smaller, not bigger, as all these new regulations start hitting home.