Before touching on the rest, I have to strongly oppose this statement:
Just a random query on LH’s website for a flight from FRA to DEN in February…one-way:
And return:
Day and night difference 
And I figure it will be same for most network carriers.
But about the general question: One has to differentiate between return trips and return bookings. Currently, the assumption is that every trip is a return trip…people will eventually want to return. True one-way trips are likely the exception in the real world, too. So the DS will always generate return requests, at least initially.
Now whether those trips are actually booked as a return is a different story and depends on a bunch of other features, like Distribution Channels or Passenger Service Systems. What you describe is people building their own itineraries instead of booking a complete trip on a single ticket via a travel agent or an airline directly. In technical terms, this would mean that AirlineSim would essentially have to allow any and all connections, at least for certain passenger types or booking requests. For the same reasons we’ve always been limiting transfers in AS, I could imagine that this would be technically unfeasible, as the possible permutations would just be too many.
But never say never…