I think it is still a very safe place to visit, and many tourists, including Americans, visit every year. Extreme things can happen anywhere. The likelihood of getting mugged I'd say is effectively zero, at least compared to London or Barcelona.
Reading this made me have to ponder the interesting fact that this is several thousand less than the number of people killed by militant Islamists in the city I live in (New York) since I moved here.
https://en.m.wikipedia.org/wiki/2018_Tajikistan_tourist_atta...
I don't think they have. It also wouldn't really make sense for them to do that. The Taliban mostly have issues with Iran and Pakistan so you will see conflicts with these nations most often in the news. I've never heard of them in conflict with any of the other stans. Badakhshan is also quite distant from the core of Taliban power which is mostly in the South. Northern Afghanistan is traditionally Northern Alliance territory.
As of last year but probably since the Taliban came to power, Tajikistan has has military checkpoints along the border. Also, I don't know about for all seasons but during the summer, the river seemed too fast to be crossable along most parts of the border.