So this is something I've been wondering for a while and I've gathered some evidence: My first thought was that WCUSA is based during the mid-eighties because of the Pigeon sale billboard and since Pigeons were built from 1982-1989. I thought my quest was over with a simple answer like this but then I noticed some more billboards such as a board with a Barstow with the captions "Unleash the beast" on the bottom. So maybe it's at a time where the Barstow was still popular but was slowly being killed off. 1982 seemed to fit the year. On another board was an advertisement for a movie called "The Explodening" which pictures a Grand Marshal. The Grand Marshal was first produced in 1990 so maybe there is a pigeon sale because there has been an entire year since the pigeon was sold and the company is trying to clear them out. I guess the Barstow board was for a movie (Since WCUSA is based in SoCal) I also noticed the WCUSA seems to be the only place with a running Nodeoline gas station the gas station in ECUSA is not Nodeoline run but just has regular BeamNG logos on it. The Nodeoline gas station is also very 1950s styled. So the year is now at least 1990. But this is also incorrect because there are advertisements about cell-phone data plans. The board I am talking about seems to be a relatively modern phone (Looks like an iPhone 3g or a Samsung S1) the 3G was released on June 9th,2008. This makes our year at least 2008. But there is also a tablet advertisement not far from the data plan board. It seems to be an I-Pad which was released in 2010. This is the newest thing I could find in a short search around the map. So the year is now 2010, But why would someone be selling Pigeons in 2010? That's a 27-year difference. The Grand-Marshal and Barstow Bill-Boards could be passed off as just up-coming movies. Maybe WCUSA is an alternate dimension where modern smartphones and tablets exist but vehicles are only being built with the standards of the early 1990s? Images
Used cars exist, the Grand Marshal and Barstow Bill-Boards are likely movie posters or just for show above a car repair shop, buildings from the 50s, 60s, 70s etc are everywhere, there are also many modern buildings. Also gasoline prices match modern day California exactly. Safe to say with the modern billboards and setting that its set in modern day and you're overthinking it a bit.
Back when DRI existed (Rest in peace DRI, you will rest in my backup folder) the Nodeoline station was abandoned. There were some tablets pre-iPad days that were incredibly basic, a few years later followed by ones that run Windows XP. There were some touch screen phones that weren't smartphones too. However, the plates expire 2018. Also there are a lot of budget car dealers that sell old cars. In conclusion, BeamNG takes place in an alternative universe where years procede like this: 2008>1987>1998>2016>2002>2017.
I noticed that expiration date is changing. I get 2019 on blue sticker. I read that you need renew it after 8 years. So it can't be set before 2002 and not after 2018 (otherwise we'll driving on expired plates) so probably it is 2017-2018 what make sense. We have modern cars so it would be strange to have map set in times where we wouldn't able to use some cars from, still, short list.
Nissan dealerships did a thing in the 90s where you could buy a brand new 70s 240/fairlady z. I'm guessing all the cars in BeamNG are like that. It's just a car lover's world. Disclaimer: this may have taken place in Japan? Can't recall off the top of my head.
Or the Pigeons belonged to some company (school district, etc.) and are being sold off, now that they're worn. Or nobody bothered to replace the billboard in the ghetto, and simply abandoned the board.
I think it's timeless. A timeless classic if you will. I think the idea is imagination. I think it's any year you want.
It's continuously in present day, since the randomization of the license plate registration stickers seems to draw from the real date. A car registered in the month of August or October would have a 2018 registration sticker, but one that is registered in January or February would have a 2019 one, like they would in real life. Proof:
.... so it's a sticker that's stating the date that it's inspected in last or the year that it's good to, which if it says 2019 is more likely a registration tab. Either way, clearly that means it's current times. Edit: I honestly can't tell if you're being facetious because of California emissions laws, or if you honestly don't want to believe that it's an obvious registration month and year. I live up in Wisconsin and our tabs look identical.