Here is a couple of reasons why it would make sense to have Deadpool appear on the show. Plus it is a total possibility especially if the upcoming Deadpool movie does really well.
Deadpool actually worked for Kingpin before Tolliver. It didn't last too long though...
2. Typhoid Mary
They both have their weird relationship with Typhoid Mary. It would be crazy to see her on the show. I wonder who would be a good actress for her...
They are either friends, partners or enemies. Personally I think they just enjoy fighting each other. We all know Bullseye (great foe of Daredevil) will eventually be on the show...so why not Deadpool?
Yes I just listed Daredevil....they have been in and out of issues with each other since 1997. So would it really be such a shocker to see them duke it out on Netflix?
5. Marvel Studios and Netflix
Granted that all of Marvel's characters belong to either 20th Century Fox, Sony or Disney (which owns all of Marvel)....Daredevil is strictly in Marvel Studios for now so anything is possible, he was owned my 20th Century Fox. However if Daredevil doesn't continue to come out with multiple seaons on Netflix, they did talk about creating The Defenders in a similar way to how The Avengers were formed. All characters get their own show to eventually form a Defenders show.
COME ON MARVEL AND FOX MAKE THIS HAPPEN!!!!!!