Well, the Duffer brothers have said repeatedly that they're not viewing it as a second season but a sequel, if they get another season from Netflix (yeah right). If you read any of their interviews, they envisioned Stranger Things as an 8 hour movie, which it totally felt like to me. They've also mentioned the Harry Potter model in terms of the kids all growing up over time and running into adventures etc. I think it can totally work. Remember, they've just introduced the fact that children were experimented on and at least one of them, developed super powers. Not to mention the ability to reach other dimensions. There are many ways they can go with this and keep it fresh. Pretty much nothing is off the table.
When I first finished the season, I initially thought it should be anthology as well. But the more I thought about it, the more I wanted to see more of these characters. The danger with anthology is that you run the risk of becoming True Detective and almost killing the franchise (rumors out there that they may bring back Rust Cohle) or you can become Fargo, and do well. Either could happen or you could land somewhere in between like AHS which is a new story, but re-uses actors with varying results.
The dilemma with Stranger Things is you have a show where undoubtedly the stars are the kids and their chemistry. David Harbour was good and I was happy with Winona as well and Matthew Modine, but if you go anthology and it doesn't work out, the chances of getting all those young actors together again to try and revive the magic for a season 3, if it gets that far, is going to be slim. Whereas if you continue with this cast, and have a middling season 2, introducing a new story/cast in season 3 wouldn't be too far fetched with the 8 hour movie model. Either way, the Duffer brothers have been pretty clear about their vision, regardless of our speculation.