Ok so hear me out here, but I think William from the new season of Arrow could still have a chance at being Connor Hawke from the comics. This is all based on theory, but I think makes a lot of sense.
Ok well with Time travel being a big part of the Flarrow-verse now what with Legends of Tomorrow, think. So imagine that soon after Malcolm Merlyn brings Vandal Savage back from the dead, he'd want revenge on those who killed him. Well perhaps he finds out about William and his mother while looking into the lives of Barry and Oliver. Or even in the distant future goes back to kill them, or just the mother.
But anywho, once Vandal arrives, he kills Williams mother and leaves him struggling for life in the remains of his childhood home in Central City. Barry soon finds the child and immediately tells Oliver the news. Oliver then takes William in as his own and breaks the news to him. Now, for the protection of the child, Oliver changes his name to Connor Hawke, the one to take up Oliver's hood when his time is up, and possibly even one to fight with the legends.
A second theory here, would be that perhaps Damien Darhk find out about Oliver's connection with Williams mother and has her killed by a hired assassin, still having the same after affect, and would also perhaps he the big death on Arrow that maybe Williams mother grew a bit closer to some people on team Arrow after some visitation rights were set down.
Now again this is all theory and is not official by any means, but I hope you all enjoyed it