I imagine the harder part is getting approval from the organizations that administer standardized tests like College Board and the states themselves.
Calculators used in university entrance examinations must be approved and certified by THE COLLEGE BOARD™, who will only approve specific models and not workalikes. The stated reason for this is to prevent cheating, but as usual the creation of monopolies who can then charge what they like is a nice side benefit, if not the primary benefit.
My kids are in high school now and it seems like what the tests are really measuring is the ability for the kids to take a test. The SAT feels especially useless as an indicator of anything other than that.
But on the other, there are a newer entries on the list that seem totally unrelated to the incumbents like Casio and HP, like this one:
It makes me wonder what the actual certification process looks like, maybe it's just adding things like exam mode and presenting it to the board