As someone whose 9 month old DS is EBF, I'm interested to see what happens to my breasts later on, after I've stopped (whenever that is).
Unless they are full to bursting, which hardly every happens these days, they are definitely less firm than they were pre-preg - larger, but saggier. Given the tendency of the body to stretch and sag as it gets older, I'd be surprised if these effects were reversed, but let's see. As others have said, it must depend on the individual a lot. I had no stretch marks during pregnancy - luck of the draw, isn't it.
I'm sceptical of the idea that it's just pregnancy that affects the shape of breasts. I don't find that a reason NOT to bf, I just don't really believe it. My mother's nipples were permanently slightly more drawn out after BF-ing her 2 DDs, and I can see a change in mine, they stick out more now. I would assume that after 2 bouts of mastitis, all the associated massaging and pumping, the early pattern of engorgement and emptying, that it would be stranger for breasts to emerge totally unaffected than bear some signs of their experience. It's an extended physiological process - it seems odd for the human body to have no 'record' of it.
I am happy to admit 2 things - one is that this reminds me a little of the oft repeated line about changes to the pelvic floor all being the result of pregnany, not vaginal birth. This is obviously nonsense, and irritates the crap out of me hearing it being blithely repeated all over birth boards.
The second thing - as I say, I am EBF-ing my DS, and have no plans to stop any time soon - but I actually feel sad and a little angry about how much a lot of the difficulties and sheer grind of early BF-ing were glossed over when I was being encouraged to BF, before DS was born. I think a 'soft sell' for BF-ing doesn't work, and backfires horribly when new mums find it hard going. And stop, because they think it should be easier, and there's something wrong with them.
BF-ing is best for babies - that's why I'm doing it. But the most vocal (and entertaining) session in my BF supprt group was when the group as a whole asked HVs why they hadn't been told about certain things in advance (cluster feeding, for example) - and HVs got defensive and said they weren't 'allowed' to say anything 'negative' about BF-ing in case it put women off! A few of us pointed out that being REALISTIC wasn't being negative, and overly rosy portraits of BF-ing make wome MORE likely to give up.
I'm not suggesting 'may cause drooping!' is part of advance info about BF-ing, btw! just that is someone asks if their breasts might change shape at all, it makes much more sense to say it probably varies from woman to woman, and things like excessive weight gain/loss and exercising without a good bra are more likely to cause stretching and shape change. In all honesty, when someone just says NO, IT DOESN'T AFFECT THEM AT ALL! it makes me a bit mistrustful of anything else they might have to say about BF-ing.
So yeah, I probably have a couple of ishoos, and no one needs to get angry with me in pointing them out, please. In the absence of some good large scale research that indicates breasts experience no shape change after BR-ing, then common sense tells me there must be some change. It's likely to vary from individual to individual, but there are very few big physical processes we go through and emerge totally unchanged. For me, that's no reason at all not to BF, it's just part and parcel of it all. Doesn't seem hugely unreasonable to me.