I'm super confused as to how they arrived at the $125,000 number,

Because it covers 80% of the United States, or four quintiles. Quintiles are big in policy. And because it's the 24% head-of-household income tax bracket.

and why it isn't scaled to a cutoff.

Because they want bumper-sticker simple going into the midterms and they don't want to penalize higher-paying degrees. If you spent $200k getting a poetry degree from Vassar, $100k getting an engineering degree from Georgia Tech or $20k getting an AA in accounting from the community college, you get $10k. 'member GWB's "have a playstation" tax rebate? same-same.

If I make $125,001, do I not qualify?

You do not. If you make $100k, having $10k of student loan debt forgiven is "cheers." If you make $40k a year, having $10k worth of student loan debt forgiven is potentially life-changing. If they put the cutoff at "poverty line plus some arbitrary number" there'd be accusations of class warfare.

Let's be honest. If you make $125k, you have a fuckton more than $10k worth of student loan debt. If you make around $125k, you now have eight months to shave a little bit of taxable income in order to get your magic number. Hire an accountant and STFU. Meanwhile the vast, overwhelming sea of student loan borrowers, who have less than $25k in debt and are largely reliant on student loans, get their debt completely wiped out.

What if I'm a physician in residency and I make $60k, but I'm going to make $300,000 next year?

Then $10k is $5k less than the $15k lid you're going to be paying if you do income-based repayment so you also need to STFU because that number has come down by like 80% or some shit. Also, if you're a resident? you already have like $300k in student loans and fuckin' $10k is yours anyway.

What if I'm enrolling in college this year at a $50k/yr university?

Then any future $10k a year forgiveness is going to be the equivalent of like half of a minor in something nobody cares about focus, man.

All-in-all I think this is moronic at best.

LOL you're establishing a biomedical startup. Your side hustle has an S1c. Nobody cares what you think.

Just change the law to make student loan dischargeable in bankruptcy court and get on with it.

Then you get to deal with the nightmare that is bankruptcy court. Prolly wanna reform that first, chief. Or wait a minute - do you want to shine a light on how 46% of bankruptcy cases are related to medical debt? I dunno, homey, that sounds like 2nd term shit. Maybe get the first one first.

$10k for everyone middle class, $25k for everyone with stafford loans is a fucking jubilee. It's a jubilee for people who file 1040EZ, for people who drive Uber on weekends, whose dreams have become an Etsy shop. Frankly? It allows people to take the money they were throwing at student loans, which paid for tuition, and throw it at credit cards, which paid for living expenses.

There's zero basis for trickle-down economics. There's plenty of basis for trickle-up. This is trickle-up, and it's designed for the same part of the brain that likes "a chicken in every pot."