I think it’s only natural, given the level of technology and advancement in the Beyond universe, to up it a few years more at this point. I think it’s more believable that in Damian’s old age, forced into retirement, we’d have a story about Terry stumbling into the Batcave than we do Bruce’s. With his millions of children already taking roost in Wayne Manor.
I also think that’d be an interesting dynamic for an AU. Cadmus, or whoever, thinks that there’s a need for the “real" Batman to be around, sometime during Damian’s time in the cowl, and makes a half-clone of his father, Damian’s half-brother, who he then ends up meeting under complete coincidence, who he gives the mantle under complete coincidence, and who he ends up being a second father to before ever realizing who they really are to each other.
Don’t get me wrong, for all of my gripes with the Beyond universe, it works so well within itself that its amazing, and the bond between Bruce and Terry is incredibly powerful to me.
Unlike Damian & Terry, though, I do think that Bruce & Terry actually lost a lot more of its potential and power when it was revealed “oh they were biologically related all along!” in “Epilogue”, where as with Damian his whole development as a character was coming to terms with the fact that blood doesn’t give anyone a family or birthright, it’s everything else. So it’s more interesting to me to have Damian build this relationship with someone and then have it tested by revealing their blood relations than it would be for Bruce.
Again, to me.
Of course I’ve got at least ten ways I’ve been trying to fit the Beyond canon & characters into the main ‘verse so I’m always look at these things.