I really enjoyed it.
I don't see why Earth-23 Superman shouldn't work. Why is the idea any less credible than Classic Earth 2 where Clark was Editor of the Daily Star. Or bronze age as a tv presenter at WGBS? Or Earth 22 for that matter.
For me it was self explanatory that having a closet full of Cal Ellis doubles he could be in two places at once.
So they look alike - it doesn't amount to much when you can be seen together - an old Superman trope.
Do you understand why Wonder Woman considered him wrong to be President, and why we consider it morally unsound at best?
To be President of the United States, you have to be born in the United States. I don't nessecarily think that's a fair law, but it is the law. Superman being a journalist or editor who who's willing to break some laws to get the story isn't half as morally unsound as a guy who cannot legally be President conning his way into office by giving an alien robot most of the Presidential duties.
It isn't an issue of being in two places at once. It also doesn't help that unlike Kent and his Superman, Ellis and his Superman literally look exactly the same, but that's ore of a logic issue.
Of course I'm willing to accept the character, and I'm even willing to accept the law-breaking, but it's not a good habit for
President Superman of all people, and I suspect that he's is going to go off the deep end the next time we see him.
I do see that - it's however only a magnification of the conundrum Clark Kent presents. Kent is a lie, always has been, when he walks he pretends he can't fly - and so on.
I'm from the UK. So I have a different perspective probably. TBH before his troubles, and had Arnold been a successful Governator it was reported here that it was conceivable that the birth law might be changed to enable him to run. As already said the laws in E23 may already be different. Even so...
We don't know the moral imperative that lead to Ellis to run for office - Morrison has to deliver that. From Ellis's perspective - that of naturalised American, who experienced prejudice due to race, I can believe he'd believe the law is unfair and unjust, delivering a moral imperative to ignore it, especially if it - eg - stopped Luthor/Morgan Edge/Other evil been elected President.
For me I didn't have my suspension of disbelief threatened by the fact Superman / POTUS look alike for the reason I gave. It maybe Morrison will give this more attention and add something to mix.
There is room to explore why Head of State Superman isn't a good idea, it's been done before IIRC more than once. It's one the guiding principals of Jeffersonian Democracy - separation of powers.