whoa. the vibe of the show would be 100% different if it stuck to that original story
UA being a university would have been fine tho
Other stuff about the one-shot: instead of All Might, there was a legendary hero named Positive who retired and disappeared one day. Midoriya realizes that another hero (Snipe) is actually Positive in a new guise; Positive had a bad run in with a bad guy that left him injured and traumatized, so he took to wearing a mask and using guns to keep from direct fighting.
Even when Horikoshi moved to the high school setting, it was going to be a bit edgier when you look at the concepts he released. All of the characters looked a bit older or mature, Midoriya (Yamikumo then) had hair over one eye (he looked like the Persona 3 protagonist with curlier hair) and he was going to be a Quirkless gadget based hero named Kid Fiend (his bunny ears and smile mouth guard were more like horns and fangs, and his color scheme was red)
Other weird tidbits:
-Uraraka was originally Mt. Lady, but Horikoshi thought that giving her a power that would constantly break stuff and be embarrassing was out of place. Her design elements went to multiple other characters.
-There's an early concept of Iida's costume or design where he looked like a skeletal dog or something. I can't tell if it was just his costume or if he was going to be way more of a mutant.
-Kaminari looked like an outright villain with long hair slicked back and a look like a street punk
-Tsuyu and Hagakure were originally boys (Horikoshi wanted to write a frog person character for a long time) and changed to girls to balance out the class. Tsuyu was also less overtly froglike and was supposed to have a more downbeat gloomy personality
-Present Mic was just supposed to be some random fat old guy who made announcements before Horikoshi made him a high energy hero
-All Might's V iconography was going to be a mask over his eyes before it was his hair
-Endeavour was going to be a teacher but Horikoshi thought it would make UA way too overpowered in fights against villains
-Midnight was going to be 1-A's homeroom teacher