My dd is 28 months and still nursing 4-5 times throughout the day. To be honest, at times it is quite painful and I don't enjoy it at all. The nipple soreness comes and goes. I also am experiencing nursing aversion, but is difficult. However, dd still really needs to nurse. She loves to do it, and I think it really makes her feel comforted and loved, so we still do it. However, I do put limits on it. I nightweaned her a few months ago, so she doensn't nurse at night anymore. And, during the day I nurse her, but when it starts to be really uncomfortable or I am really having nursing averision I tell her she can nurse for 20 more seconds and then we will do X. That seems to work pretty well.
We will probably tandem. I can't imagine dd giving up nursing, but you never know. I also think it will help a lot with sibling rivarly. At this stage, if we were to wean, I am sure dd would still remember nursing as what she did and as "her" thing, so I think allowing her to tandem will help.