Well, technically, it can be done, since PIREPS and schedules are separate from each other. But financials bring a layer to it, since when you file a PIREP, it looks at the schedule to determine the price and the load factor for the flight. That's a one time lookup.
So there would need to be a way to translate that information without it being on a schedule to look it up. And then a way to figure out/translate flight numbers and codes. If people have suggestions, I'm open to them.
One way would be to attach the load and price to an aircraft - but different routes have different prices, even though it's the same aircraft. Could be a fallback maybe, if there is no schedule, then refer to an aircraft. But, different aircraft can be used for a flight, but perhaps it'll use the registered aircraft.
Then a case for... if there's a free flight, and someone enters a code + flight number, and it conflicts with a scheduled flight...
It can be done, just needs to be hashed out.
But I'm open to ideas/suggestions (perhaps for the next update)