Thats a good theory, and makes sense. I still want Oliver to face Grant Wilson, dressed as Deathstroke, to make the audience think its Slade only to reveal its Slade's son. Then it is revealed in flashbacks that Grant sneaked into the program and got injected with the blood all in an effort to be the son his father always wanted. It wouldn't take away from what I know see as a good reason to be mad (like you said) but it would also give him more reason if Oliver was seen as responsible for Grant's death.
Grant thinks Slade is dead and is maybe contacted by Brother Blood who is trying to gain an upper hand or something. There is a connection to Adeline and HIVE as well. And brings Grant in to hopefully recreate Slade so he wont have to use him. It could also turn out that the real person behind all this is Adeline herself who knows Slade is alive but hates him. But these are just ideas.
OK, so now I am just rambling off my own ideas but how about this:
As of right now the audience knows there is a group called HIVE. They also know that Slade controls Brother Blood, using him to create Super Soldiers to attack Oliver. What could be revealed is that Brother Blood is also working for HIVE (first thought to be its leader) and HIVE's leader is Adeline Kane (formerly Wilson) who tells her son Grant that Slade his father died on the island at the hands of Oliver Queen/Green Arrow. She sends him to Brother Blood to become a Super Soldier. He dresses as Deathstroke/Wintergreen and goes after Oliver. It is revealed that it is not Slade or Winter but Grant and at the end of the fight Grant dies. Slade hears about his death and is angry over Oliver's involvement and Brother Blood's. It was all orchestrated by Adeline Kane who also has another son, Joseph. She is targeting both Oliver and Slade in an effort to control HIVE and the soon to be Super Soldier population. Her other son Joseph is more of a Wild Card, a double agent. He goes by the name Jericho while communicating with Oliver. During his efforts to help he is injected with some experimental blood and gains his own power to control other's bodies. But his efforts to help everyone, help his mother in her plans, help Oliver in his plans, and help his father in his plans, ends up costing him is life.
After both Adeline and Slade are killed off pr gone and after maybe a season or two Rose Wilson shows up as the new Deathstroke, angry at the vigilante Green Arrow for murdering her father, and she finds out that he also is responsible for the deaths of her brother's Joseph and Grant.
I think Slade is a great character with a great dysfunctional family. I also would like his wife Adeline, his son Joseph, and his daughter Rose, to eventually show up on Arrow too.
But I like the story idea I have for Grant.
Rose I can see showing up seasons later to avenger her father, and maybe even stabbing her eye to be like him.
Michelle Trachtenberg (?) from Buffy and Gossip Girl as Rose
Stephanie Romanov (from Angel) could play Adeline