I was at O Scale West in Feb. I saw a lot of modern engines and cars. I think that people who want modern diesels should check out MTH's 3/2 rail offerings. Many of the MTH engines can be ordered in the 2-rail version. The new MTH PS-3 engines come with DCC installed. MTH builds both 2 and 4 axel diesels.
I also saw inter-modal cars and modern covered hoppers by Lionel and MTH. All of these cars appeared to be excellent models to me. I don't count rivets. I also saw some modern tank cars and aluminum hoppers. Yes, they would need to be converted to 2-rail. Most of the avid 2-rail hobbyists have the skill to do their own conversions.
There was a fellow at O Scale West who was selling converted boxcars and other 1950s era cars. He appeared to be doing a brisk business. Perhaps someone could contact him about converting modern equipment.
I really wonder if there is a large demand for modern equipment in O scale? Most of the guys at O Scale West are 60 plus years old. I am in the 70 + group. The stuff that sells seems to be transition era equipment. I went on the layout tours. There was not a single modern era O scale layout on the tour schedule. All of the O scale layouts that I visited are running steam. I don't know of a single modern era O scale layout being built or being operated anywhere in the SF Bay Area and I have visited most of the O scale clubs and layouts in this area. Come to think of it, I don't recall seeing photos of a modern era layout being posted on this forum. Are any modern O scale layouts being built anywhere?
I have the current issue of "O Scale Trains Magazine March/April 2015" in front of me. The front cover has a photo of an O-6-O steam engine. The layout article is about a PRR steam era layout. The main review is of the 3rd Rail N&W Jawn Henry steam turbine. There is no modern era in this issue of the of the main 2-rail magazine.
I think that people who want modern equipment are going to have to look at converting Lionel and MTH equipment to 2-rail for the foreseeable future. Atlas appears to making only small quantities of O scale. Weaver is concentrating on transition era cars. 3rd Rail is making transition era F units, etc., because that it what sells.
Joe