Which of the following is a vital aspect of an IFR flight plan?

A vital aspect of an IFR flight plan is the pilot's intended flight path and expected altitudes. This information is crucial because it allows air traffic control to understand the intended route and altitude, ensuring safe separation between aircraft. It helps in coordinating traffic along different airways and assists in efficient airspace management. The planned path must align with existing air traffic routes and must also account for airspace restrictions and the aircraft's performance capabilities.

While other considerations in the options have their importance, they do not hold the same critical role in the IFR flight plan submission. For instance, GPS coordinates for airports may enhance navigation accuracy but are not a fundamental requirement for an IFR flight plan. Current weather forecasts can influence flight decisions but are subject to change, whereas the intended flight path and altitudes are integral for executing the flight plan safely. Weight and fuel capacity, while important for operational planning, are not included within the structure of an IFR flight plan itself.