Lyxen
Great Old One
Not really? Unless you change point buy to make it so that you have much less points to distribute, getting a high casting or Strength / Dex score and then getting a high Con score is still going to be fairly optimal. If Con becomes even more important, then build diversity will decrease because getting a high Con to survive will be even more important. You won't want to skip out of it. Without Con, a lot of classes get more flexibility.
That's assuming that you can get who high scores. But if you already need two in your class core stats (because we want classes to be less SAD), then having Con to worry about will have you make hard choices between survival and efficiency, and that's what I think we want to have different choices matter, right ?
Dex is still going to be a priority for some classes, but it's likely you can get away with a +2 on that and spend your access points on getting better mental scores and having some extra skills.
And if Dex is not as much a god class (honestly, using Int for Initiative would not be stupid, for example), for once, and if Dex is not one of your class core skills, then you will have even harder choices to make.
Heck, now I'm confused why you mean by SAD because right now a lot of classes depending on the game ran are optimally going to invest in Con, getting it to at-least a +2 or +3. But I would still call those SAD since they're only doing that for HP.
That is the PH's perspective, but if you look at guides, they are more moderate about Con impact in general, most prefer to be really efficient with powers than survivability (which I think is a real danger, but at least you have choices).
I played wizards in BECMI/AD&D, so I know what it means, but no-one says that you have to start with only one HD. You might have you Con as starting HP, for example, or something like 4e did. There are other solutions to that specific problem.You are also going to make starting a level 1 even more lethal without further large adjustments. A 1d4 for Wizards might be appropriate, but Sorcerers are going to have a little bit too much fun being damn squishy.