That's not even mouse bastard. Rat bastard is your mom is the assassin who's been plaguing the community, thanks to magical or psionic domination by the real villain. Player characters spend weeks figuring out who's behind the murders and stake out the next victim and end up injuring and almost killing Dear Old Mom before she's unmasked. Thanksgiving will be awkward this year ...DM: "The invading army of orcs has sent a warband through the valley of Highway. Roadkill is straight in their path; your mother will be slaughtered if you don't save her." ---> This is totally cool. I mean, it's a rat bastard DM thing to do, but I approve of rat bastard DMing.
Had a similar line of thinking a while back, had a character's brother go south of the border (ie nuts) kill their dad, use magic to turn mom into a mindless killing machine and then bedded both younger sisters to progenerate the "master race". When they faced sword swinging mom, it was kind of tense around the table, when they stumbled upon the shackled "love nest" of the sisters the players howled in rage - it worked, but I was looking at the exits for quite a few moments and planning how I was going to explain to the police why, "my friends are trying to kill me..."That's not even mouse bastard. Rat bastard is your mom is the assassin who's been plaguing the community, thanks to magical or psionic domination by the real villain. Player characters spend weeks figuring out who's behind the murders and stake out the next victim and end up injuring and almost killing Dear Old Mom before she's unmasked. Thanksgiving will be awkward this year ...
I had the little sister of the ranger in my Midwood campaign -- an NPC she explicitly introduced as a foil who looked down on her woodsy sister and who dreamed of being a beautiful princess or lady in waiting -- fall under the spell of a worg sorcerer and work as a low level saboteur for a while, before things accelerated and the worg was revealed. At that point, she kidnapped the rest of the family, whom the worg intended to kill to get revenge on the ranger's father for killing the worg's family years before.
Everyone enjoyed the tween "villain" being revealed and then the creepy sequence of battling the "Big Bad Wolf" type figure and the resulting hostage situation.
Everyone had previously bought into the idea that the village was the primary setting for the early stages of the campaign and that the stakes were going to be personal for many of the adventures. That was established at the time everyone was rolling up their characters to begin with.
@J.Marley: Ya, if you want to add some new element to the world with your background, I think it would be fair game to use it. And I don't think you should just sort of dictate to the DM how you would like that to happen.

QFT.Which is another point: the players' suggestions can indeed make a GM's setting more exciting.
There has to be a happy medium: Characters need to create characters, not anonymous loners
Requiring the DM to come up with endless compelling plots that have nothing to do with the characters themselves is just as much of a cliche as the evil general being a relative of the heroes.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.