I think this is something that we forget about on the virtual stage: we can still observe through body language and backgrounds about culture and cultural differences.
The students not only get to talk to one another but also can see how their partners react to questions, how they look, and how they live.
“It’s not knowing only a language,” he says, “but also knowing how to behave and acknowledge differences—cultural differences, behavioral differences.”
I like this article even though it's from 6 years ago because it talks about the benefits to teletandem communication. I hope you are able to read it because it's from the Chronicle of Higher Education and you might need to sign up.
I like this review of Extempore a lot because it lays out all that the tool can do in a clear way. It also gives it a rating and discusses ways in which it can be used.
I came across this blog looking for communicative activities to do with students online. They have an online immersion program for several different languages but also maintain different blogs for certain audiences. This one is the "General Educator Blog." I found their content helpful and really informative.