I'm happy to be corrected if anyone has any experience with this, but I don't think soddies were that much easier to build than log cabins. It was generally that there wasn't enough good log wood in the area.
To be fair, it's a hard comparison to make because a log cabin could be anything from a dirt floor shanty with some stacked wood, to a precision-built home that could last for generations. Similarly, a well built, and maintained, soddy could be a work of art that had surprising durability, and could be boarded in, painted, and maintained. I think a crappy version of each would be a similar effort (cutting and moving sod can be an awful pain). In quick googling, it it said it would take about an acre of land to build a house the size of a 2x3 game cabin, and could be as many as 3000 bricks (about 4 inches thick, 2 feet x 2 feet in size).
In the prairies, people would upgrade (as you say), if they could afford prepared wood to be hauled in, after their first good harvest year. A lot of it has to do with the Dominion Land Survey (in Canada), and the Public Land Survey (in the US), because properties were arbitrarily placed and wood would be difficult to get in. The Metis (as well as Cree and Assiniboine), tended to property near waterbodies so it would be easier to float in timber.
When wood was available and people wanted something quick, they would built a "shanty", which means a really crappy wood framed building. Usually, there was no floor, and the timbering could be very random. If it is suitable to the game, a step below cabin could be a shanty-style building made out of boards, with a few logs.
I think I'm going to do some research on housing in Iron Age Finland, and see what was available. Regardless of how useful cabins (or other buildings) are, I really enjoy the feel of building in the game, and think it adds a lot to immersion to see people living in different dwellings. Therefore, if there were soddies (Islanders' area seems possible), then it would be an awesome addition.
Regarding maintenance: I think it would be an excellent addition one day to have things fall apart. It would be very cool if shelters collapsed frequently, and cabin walls or ceilings could fall apart periodically. I know Sami has talked about including storms one day, which could be bump up the likelihood of that occurring.