Yeah I never could figure out who the kingdom come Flash and GL were. GL seems to be Alan Scott because of his blonde hair, but then at the end of the series he represents "new oa" at the UN and his hair is now darker. The flash is still ambigious. But did anyone notice that in the scene where spectre talks of heroes hiding in past in future times, the legion is shown and with them are a superboy and a supergirl? I wonder who they are.
In the Absolute hardcover edition of
Kingdom Come it was revealed that the Legion's Superboy and Supergirl were Kon-El and Matrix, who abandoned their native present time for the far future.
There was an incident during Kon-El's
Superboy series when Ferro actually designed a
Kingdom Come Superboy uniform for him, but Matrix never donned that particular costume. However, the idea that Supergirl would permanently join the Legion
did occur in the animated
Justice League Unlimited.