Speaking to a friend of mine with experience railfanning in North America....
He normally knows what he's talking about, having been responsible for numerous books and magazines in the past, so I'm inclined to wait and see with optimistic eyes.
I've written four books and numerous articles and I've just been to the USA, and I'm still on my way back...
Most of the genset locomotives have been paid for by federal, state and local governments to reduce exhaust emissions, particularly in California. Louis Marre, author of all but the first Diesel Spotter's Guide, believes that genset locomotives are a temporary expedient.
With government subsidies, the railroads will buy these genset units but as I saw in California, they'll still use old EMDs as switchers.
Both GE and EMD are offering low emission conversions of existing locomotives using current locomotive engines, and EMD in particular have been successful in selling hundreds of these.
A number of F59 PH and F59 PHI locomotives operated by the California Government (Amtrak California, Metrolink) have been rebuilt with 710 ECO engines and can be recognised by higher roofs over the radiators. There has been little publicity about this but the locomotives with Amtrak California carry new builder's plates, decals explaining the funding and a big "eco" decal.
GE and EMD suggest that the long term repair costs of their options will be less than that of genset units.
Pacific Harbour Lines are re-engining the former EMD units fitted with MTU engines with new CAT engines with even better emissions. They wouldn't do that if it wasn't government money.....