I'm having a hard time buying the April theory. I think it's more likely the piece of concept art was a disinformation plant.
Even with the changes to the timeline, the only commonality between Cumberbatch and what little has been established or even conjectured about April is that he's British. Otherwise he's the wrong age, has a totally different history, different personality, different motivations, different everything. Certainly they could still call him Robert April (presumably after revealing that the name John Harrison is an alias) but to do so would be virtually meaningless. They might as well call him Cyrano Jones or Harry Mudd for all the relevance it has.
Then again, these are the same people who applied the name Delta Vega to a completely different planet just to give a shout-out to the relatively few people who would recognize it, so who knows?