Saudi Arabia (Arabia) Proposed Republican Flag

By overthrowing the monarchy and the royal house of Saud, they’d change the name, most probably to the Republic of Arabia. Arab Republic of Arabia wouldn't make much sense name-wise. But given the huge number of non-citizens and immigrants, the name could also be just The Arab Republic like i.e., The French Republic. The difference may be subtle, it's not entirely a matter of language-specific preference.

They'd most probably adopt the pan-Arab colours, but I find your flag is very interesting. It needs some Arabic touch though, because without it (to me personally) the flag looks like Mandela's flag for African National Congress.

The flag for the Republic of Arabia would also depend on what kind of republic would it be? A completely secular republic like i.e., Syria, Iraq, Tunisia, or an Islamic republic like i.e., Iran, Pakistan, Mauritania? Or a mixed legal system like Algeria and Egypt? IMO, secularism could only be achieved through a revolution. Getting rid of monarchy is one thing, but getting rid of Islam legally and constitutionally would truly be a radical move. Even Iraq which is nominally secular has Allahu Akbar on their flag.

So, an Islamic/MixedSystem republic it is. Then a current shahada would most probably remain on the green stripe make a claim and history connection. Without the "royal" sword, of course. Or tekbir/shahada/other styled inscription could be added to the bottom of the black stipe and at the top of the yellow stripe, like Iran’s flag. Either/or, not both, it’d be an overkill. Here's a sketch.