It's not entirely unexpected: Nelson is a key (if sometimes underutilised) element of Daredevil, the plucky and occasionally snarky law partner and best pal to Charlie Cox's Matt Murdoch. We also saw in the second season of Matt's adventures that Foggy was offered a job by Jeri Hogarth (Carrie-Anne Moss)'s law firm, so he'll be crossing over into other areas of the series' connected New York.
The news comes via Henson himself at a convention appearance, and there are no other concrete details about the big crossover other than it'll shoot later this year, bring together Cox, Jessica Jones' Krysten Ritter, Cage's Mike Colter and Fist's Finn Jones to battle some new threat. Unlike the regular shows, it appears to be more limited in episode scope with just eight planned for this first outing, and Doug Petrie and Marco Ramirez, who oversaw the second season of Daredevil, are in charge.