Yea, between 2-3 years untill Season 3 is done seems like a fair estimate.
I don't know about his steam sales, nor do I care much. Only thing I remember is that someone posted a screeny at release of Season 2 and BaD was among the top 10 games played on steam, so I guess he's doing alright.
As for Season 3, I think when its released on steam, people will purchase it, play it and write their reviews and if they're positive, DPC will probably do good regardless of the development time he needs for S3.
There was a time, when I was hoping 2 Episodes a year would be the minimum, but we are long past that and if I'm honest, as long as the content we get stays at 10-15 hours per episode to see all the content it doesnt make much of a difference to me, whenever a new episode is released I'll play it and untill then I play something else.
I can understand why people are worried, DPC, at least to some degree, sets the bar and other developers may adopt the same mentality, but I've yet to see anyone match development time vs content delivered even remotely, DPC is in a league of his own there in my opinion.
DPC has been beat in render quality, render detail, animation quality and some games have a much better, albeit more linear, story. But, at least in the other games that I play, it usually takes the developers 3 Months to release 2 hours of content or 6 months for 3-4 hours of content and as long as that doesn't happen with BaD I'm cool with waiting 8-9 months, it just has to stay the BaD quality we have become accustomed to.