Supergirl and the Rise of the Supermen

Hank Henshaw (David Harewood) growling, "I am Cyborg Superman" might have been a little on the nose but it did force him out of the obscurity of a regular-sounding human name (that only comic book fans recognize) to one of the four beings that might eventually take on the mantle of Superman (Tyler Hoechlin) upon his death.

Supergirl drops major truth bombs before major crossover event

For Superboy, you need to find someone who is ready to fight for truth and justice "my way" and would look smokin' hot in a midriff-length leather jacket.

Sure, Mon-El isn't a clone created in a lab or anything (OR IS HE?) but as someone with superpowered fists but not exactly a superpowered sense of guardianship, he matches the personality type.

[...] his drive to help people would be much more believable than just an innate sense of justice provided by Kryptonian DNA.

Kara's good-natured sexual aloofness just makes all men go weak in the knees and inspires them to be better, more dangerous people.

[...] is Guardian such an inconsequential hero that they'd use that identity as a stepping stone to Steel and discard the alter ego once the bigger arc begins?

Except for Red Tornado and, although I'm sure that bucket of bolts will be back in some form or another, it doesn't exactly have a worship-worthy level of charisma about it.

There's the possibility (in that everything is a possibility if someone has thought it) that Lena Luthor (Katie McGrath) might make a machine to take over for the Supers in the event of their untimely demise, some kind of wayward attempt at helping people to make up for the twisted Luthor history with the House of El.

Was it programmed to exact revenge on the monsters who would allow Kara or Kal to fall to Earth-terrorizing threats?

Unchecked, would Kelex, as the almost lone holder of knowledge about a doomed planet, try to remake Earth in the image of Krypton so to protect Kara?