There is a simple and surprising extension of the idea that future people matter. Possible people matter too! That is, even if it is not guaranteed that a person will exist, it still may be ethical to act upon their needs.
Even if there is only a small chance of someone existing, in the event they do exist, the decisions made before their time can have huge impacts on their welfare. This means that over the long term, neglecting possible people leads to real damage, since even a low probability event will occur given enough opportunities.
Once again, I am not saying that possible people matter as much as contemporary people! Just that they matter some amount.
This premise gives us a new view of how ethical theories must behave, weighing the needs of modern society against the needs of the future, while balancing the needs of different possible citizens that might live there.