Automotive and light/medium truck diesels with aftertreatment are pretty much universal. Only VW has a few without. Yes, the driver has to keep the "fluid" tank full - normally topped up at each oil change. But it doesn't seem to have affected overall reliability in light-medium duty engines much as long as the tank isn't allowed to go dry.

If you assume (take that word apart...)that aftertreatment will fail because nobody will keep up with the fluid requirements, then you have a self-fulfilling prophecy. It will fail, because word will get around about your assumption and your employees will make it so.

Does GE use aftertreatment on its Tier-4 engines? Supposedly they're out testing real (not just interim) Tier-4 locomotives now. They could end up the only game in town if the 710 just doesn't work, RRs refuse to go the aftertreatment route, and GE can do it without.

EPA is required by law to set and review/update emission standards. They don't dream things up just to make it difficult for makers and users. It's up to the engine/vehicle makers how they meet the standards. In the latter 1970s, most carmakers went with catalytic converters because they were the most effective way to meet the newer emission standards and improve (from the truly horrible days of 1973-75) driveability and durability. The fact that unleaded gas availability was mandated starting in the early 1970s supported conversion to catalysts, which required unleaded (or at least very low lead, for the time) fuel. Honda and a couple of Germans tried to get by without catalysts (remember CVCC and thermal reactors?), resulting in cars that ran horribly, had terrible gas mileage, and occasionally burnt up. They all went to catalyst in the next round of updates in the early 1980s. By the late 1980s, with near-universal computerized fuel injection, feedback mechanisms, and 3-way catalysts, cars became more powerful, more fuel-efficient, and more reliable than before emission controls. I suspect something similar will happen with locomotives - various approaches to start with, but based on what I've seen in the truck and stationary engine fields the aftertreatment approach will almost certainly win out eventually. Railroads will need to refill fuel, water, oil, and DEF tanks whenever they stop for "gas" as a standard practice (unless they switch to NG, which has its own issues).

As far as the ethanol thing is concerned, EPA (and ARB) frankly would rather that there not be a requirement for it in gasoline. Both are interested more in the emission performance of the gas than specifically what's in it. The ethanol mandate came primarily from Corn Belt legislators who put that into energy laws, and told EPA to enforce it, plus the experiece with MTBE which was a great fuel oxgenate (back when we really needed it to address emissions during the old-car warmup period) and really cheap for the refiners; but horrible for the groundwater. That left ethanol as the only readily available/usable oxygenate in town. Frankly, with old non-feedback, slow-lighting-catalyst cars very thin on the ground these days, ARB & EPA would rather not have to require oxygenated gas at all - it's perfectly feasible and probably cheaper for refiners to meet California (and soon nationwide) gas standards without ethanol or any other oxygenate, and ethanol also causes problems with tank and piping integrity and "soak" emissions. But the energy (Corn Belt subsidy) laws still require use of a certain (and growing) percentage of ethanol whether EPA likes it or not. Talk at your Congress Critters if you want to get rid of the ethanol mandate, not EPA, and I wish you good luck getting the Senator from ADM and the Congressman from Tyson to listen to you.