I've definitely flown with someone who overflowed and took up half of my seat as well as his own. It was NOT pleasant. The obese man didn't even slightly try to stay in his seat. His arms stuck way past the armrests and he sat spread eagle, so his legs took up half of my leg room. The only saving grace was there was a nice lady on the other side of me that didn't complain when I leaned into our shared armrest. She felt sorry for me. I support your suggestion.