I agree that 1000 hp per axle has been around on electrics for years, but simple physics limits you to only being able to use around 500 hp or 15,000 pounds tractive effort per axle (assuming 30 ton axle loading) unless a newer high adhesion system is used. But what most people (and railroads) don't pay any attention to is that these are theoretical figures. Under poor rail conditions, the ability to use the full amount of horsepower is simply not possible. We had a call from a railroad whose 50 series engine was refusing to pull more than 1/4 of its normal tonnage up a grade. By the description, it was obvious the Super Series adhesion system was severely derating trying to maintain its feet. It was finally admitted that the track inspector has liberally greased the curves before the problematic trip. As the rail cleaned up on subsequent trips, the engine was able to dig in and pull as expected.

The biggest issue with 6000 diesel-electrics in North American service is that if there were only two units on a train and one went down, the remaining unit did not have enough tractive effort to get the train up most grades. Even downgrade might be a problem if there isn't enough dynamic braking effort since most railroads don't even remember what retainers are for. If you had three 4000 hp engines instead, the failure of one unit only would result in a 1/3 loss of traction and dynamics, not to mention having more tractive effort at low speeds and less wear per traction motor. Today's 10,000+ ton trains also have to depend on the DPU units working, especially single units, because often the power must be distributed to stay within coupler limits.

My understanding is that GE's T4 GEVO does not use DEF. I'm not sure any Class 1 is willing to buy an engine that uses DEF for cross country freight service, at least not yet. GE does have a 6-cylinder GEVO at 2000 hp (too high for gensets but enough for a 4 axle) and I assume it will be T4 compliant. To my knowledge, the GEVO 6 has never been installed in a locomotive - its competition was the 8-710 which did see some loco applications. GE also acquired another engine line when they purchased a European power generating company several years ago. The Jenbacher was a natural gas design that GE converted to diesel and did use on some export locos for Europe. I haven't heard if their are any efforts to make it T4 compliant.