Something like auto resize images, Grid forum/resource layout or the add-on update notification as an example. A lot of functionality I do see being standard in IPS. I don't mind that XF might also raise the price if a lot more is added by default, I am happy to pay for it.
It is now a bit out of balance, you have certain add-ons that you just want, you build your community on this, but you are pretty much out of luck if the developer suddenly stops.
For example, I had my community leaning heavily on everything from Themehouse, and we all know how that turned out. Not very reliable.