Here are some of the guesses and thoughts from me and others.
Tracer is because she blinks like a trace round.
Widowmaker is just the spider thematic also the part where she made herself a widow by killing her husband.
Reaper was given to Reyes because people say that he looks like the grim reaper.
Some names like Pharah and Zarya are nicknames to pronounce their names easier, fareeha amari and alexandra zaryanova, respectively.
Bastion because he is made to defend something.
Genji and Hanzo are first names, last name is shimada, and Hanzo is from Hittori Hanzo and Genji is from Hakura Genji. Hittori Hanzo is the most badass ninja in Japan history.
McCree full name is Jesse McCree, McCree’s name might be influenced by an old game “Mad Dog McCree”
Zenyatta is Zen but with a monk like twist, and his last name is for siddartha. Siddharta Gautama, also known as the Buddha. It’s the name of the prophet/founder of Buddhism. Zenyatta’s full name is Zenyatta Tekharta and the Tekharta is a stylistic reference to that.
Considering how Mercy‘s name is Angela, I wouldn’t doubt it probably the whole “merciful angel” thematic or probably just because she heals everything.
Soldier 76 is a moniker given to morrison because he wears that 76ers jacket. But is there more meaning for 76 the number? Would love to know that.
Symmetra is a moniker, real name is Satya Vaswani. And symmetra is like a title I think. It’s just the whole orderliness thing I think. Symmetry is one of the most common and appreciable forms of order in our lives and Symmetra is all about order character-wise.
Reinhardt is the first name of Reinhardt Wilhelm, a German name I think. And there is a hard in Reinhardt, could be presenting his powerful hammer?
Roadhog lawless motorist and hog means pig.
D.VA sounds like an operation code for a war machine. Since she was a former esport gamer, the VA makes it cute. Kind of? 😐
Winston is pretty much a human name. Winston was raised up by his doctor so I think when the doctor tried to name him, he wanted it to be human and be humane.
Torbjorn is the name of the Sweden mechanic Torbjörn Lindholm. Sounds like a Sweden name maybe?
Mei looks like a common Chinese name – after the family name. The Chinese equivalent character is 美.
Junkrat lived with junkers from where he’s from, it’s like rat that scavenges food in junks.
Lució sounds like a Brazil name, since most of the people speak Brazilian-Portuguese and Spanish, the ó sounds like a Spaniard.