It’s not as outlandish of an idea as you may think! I discovered very similar seats on Canada’s Via Rail from Ottawa to Montreal about a year ago. The underseat storage was angled in the opposite direction from your sketch, ie. your bag goes angled under the seat you’re sitting on, but otherwise it was the same idea.

Unfortunately it didn’t strike me as particularly effective. My small roller bag didn’t fit. Perhaps the underseat volume was larger than average but usable volume wasn’t. More importantly, it seemed that cleaning the storage area was impractical due to the odd angle.

I can’t post pictures but you can search Via Rail Renaissance car walkthroughs on YouTube. Most Via cars have normal seats, and at this point I don’t know if the Renaissance cars still operate. They’re the ones with 1-2 economy seats.