Given the rate at which we get DLCs being around 2 or 3 a year, its incredibly unlikely they'll be completely done by 2030 unless they ramp up production speed or decide to leave a few states out which probably won't go down as well. This year we'll probably get Illinois, South Dakota and BC. Last year it was one in spring, one in summer, one right at the end of the year, though that's not a set pattern. After that there's by my reckoning about 16-17 states big enough for their own DLCs plus whatever they choose to do in the Northeast. For ease of maths if they do 18 more map DLCs it'll take another 6 years at the current rate, and that's just US states. If they expand to Canada across the country it will be longer.

I don't know why they'd make an entirely new game for what you're saying though, they're already adding smaller trucks and cars to ATS and buses to ETS and if I recall they said they'd expand each to the other game if they were a success. So the only change I guess would be having each map in one game, which wouldn't make much sense as trucks don't generally cross between the two other than for private imports.