It is hard to say definitively because there is no data sheet released for the Apollo4 yet. I would not expect it to be much different from a programming perspective. Also, the Ambiq HAL has done a pretty good job so far at abstracting away the differences between the other members of the Ambiq processor family, so the HAL should take care of a lot of the changes.
The big difference is for Sparkfun, not us. The Apollo4 comes in a different physical package meaning that Sparkfun needs to redesign their module. The Apollo4 has an extra 23 pins and is a different shape. That said, from a user perspective, there might be a potential advantage if Sparkfun could use the same module pinout as they ship now. That would allow for easy migration from Apollo3 to Apollo 4. On the other hand, that would hobble the Apollo4 module because it would mean that not all of its pins would be available at the module pinout. And from a practical perspective, it looks like Sparkfun had quite a time getting the Apollo3 pins out to the module pins in the first place. If the Apollo 4 pinout is much different, it might be an impossible task to make the module pinout match. My expectation is that there would be a new module. And if that’s the case, then I would vote for Sparkfun to add the 32KHz Xtal and xtal caps to the module instead of making all of us put it on our motherboards.