Not sure that I agree. The ITN(Interplanetary Transfer Network) seems like the main reason to include Lagrangian mechanics. The transfer times aren't that much longer than the amount of time that people spend waiting around for hohmann transfer window, and they would allow extremely interesting craft. For example, the genesis mission used ITN to get to L1 and back in 2.5 years(much of which was normal mission operation, not transfer) and propulsion was only 5% of their mass! Imagine the possibilities for interesting missions when your fuel requirements are so low. And yes, the math will be hard for players, but there is no reason to think that people won't develop interesting tools to help with this in the same way that they built the hohmann transfer calculator.