I too wonder the same thing because I have low supply and have to supplement ds. Ironically I dreamt about this very thing. i think I have IGT, so one side produces next to nothing and the other side possible 1/2 ounce an hour, well that's how much i can pump. Anyway in my dream, lol--kind of funny that I would dream about this last night, well in the dream I let ds nurse from the the low producing side and the new baby from the better prducing side, which in fact, if ds does happen to still be nursing is what I would probably do because I contemplate even letting the next future baby take the right side, because it produces so little now and also if ds was to to nurse from it, it would ultimately increase my let down and supply on the left side, kwim? I know that I will always give the left side first, because with ds I did what some people say to do, to give the less producer first and more often, etc. and it will increase the supply, well the made ds get dehydrated, so now I always offer the left side first and ds will only take the right side for a minute or two, needless to say I am lop-sided
Also you could let your ds drink after your future lo to help increase the supply.
I suppose every situation would be different though. I have to supp ds with about 18 ounces of formula a day, some people more, some less. Also take in mind that your ds could self wean when you are pg.
Anywho--just wanted to say our ds's are a week apart!
semi crunchy single student super mama to DS 7 and DD 3. Falling in with single super dad to DD5 and DD2