So, I obviously want Q to be a brother (not long lost, just conveniently unmentioned on Sherlock). That's definite. What I'm toying with is combining the ideas of Q as the Holmes brother and M as the Holmes' mother (because that totally makes sense to me, too). However, combining the two ideas poses a slight challenge in terms of a Q/M relationship.
I think I can make it work by saying that M has always been careful about not speaking about her children and keeping them off the map and so therefore not able to be targeted. It could extend to work, which would mean that Q and M wouldn't show any irregular affection to one another, at least not in the presence of others. I don't think they have a scene in Skyfall together, so that doesn't particularly matter.
The problem comes along with the fact that Q is basically responsible for M's death (not totally responsible, but how a son would look on the situation). It was his security protocols Silva got through, it was he who plugged the computer into the main systems, allowing Silva to escape, and then he placed a trail of markers leading to M so Silva could find her, without arguing too much about it. It's a LOT of onus to put on Q, and I'm not sure if I want that much angst.
There is the option of making Q a half-brother on the Holmes side, but that's a whole other angst thing. I generally prefer to keep my Holmeses eccentric, but ultimately pretty functional. I don't know if I want to throw affairs and love children in there. Unless M and Mr Holmes got divorced and he remarried soon after and had Q. Because, by the age I usually put Sherlock at (somewhere around 34) and Ben Whishaw's age (32, though he looks about twelve), I'd say the gap between them is only two or three years.
So, thoughts, questions concerns?