oh my god you absolute madman you actually did it!
feedback: so I gave it a shot in creative mode. filled a 2-4 train full of IR2 iron ingots, and slammed into the block at full speed. the game promptly became a slideshow lol. projectiles are definitely slowing it down, but placing the items is even worse lol. granted, I had nothing to store it - I'm guessing only the iron chests without tops work? about to see if the lag is more manageable with tons of chests placed to store the goods
EDIT: so having chests placed to hold the items help with the lag a lot. now, for some more feedback.
can you set it up so that the block of concrete shows an estimate of where the items drop? I placed a ton of chests in my test (https://puu.sh/IoTmQ/6fbeb9addf.png) because I wasn't sure where I'd need them, yet I still didn't manage to collect a good portion due to falling off the sides. I did manage to sorta find the splash zone, though (https://puu.sh/IoTo5/51489861b0.jpg).
still, as you can see here (https://puu.sh/IoToz/415d7410d6.png) a lot of chests in the splash zone didn't manage to grab the falling items, which slipped between the chests (and if this didn't happen in your testing, maybe it's because of squeak through?) meaning I can't really rely on collecting the goods here. and it wasn't because the chests were full, either (https://puu.sh/IoTob/0c58e4183e.png). granted, the fact that the only chests that can collect this are the 1 tile iron chests that don't interact with the logistics network means I can't really collect goods this way anyway (inserters can't reach the chests in the middle of the splash zone). as far as I can see, the best use of this would be to landfill a bit of a body of water to make rails going to the center, place it there, and have the train dump tons of nuclear fuel into the ocean as a big middle finger to the biters, but even then, some of the stuff will end up on the side of the tracks instead of in the water (and it'd probably lag like hell lol) (actually, scratch that, it lags a lot, and many items end up on land nowhere near the splash zone lol https://puu.sh/IoTvq/5f7000d9d1.png) so I wouldn't recommend using it like that, either.
could you change the impact unloader into a sort of unloading site? for example, have it be a block of concrete with a big ol chest behind it? and attach a giant basketball hoop on top for the memes. then instead of having items spray wildly, have them get dumped into the backetball hoop? it should be easier to make work, definitely easier on the lag, would be even sillier, and even be an actually usable way to do train unloading. granted, it might look weird if a long train pulls into the concrete slowly yet somehow having the rear carts dumping into the hoop way up front despite there being not nearly enough inertia for that to happen