Unfortunately, I'm talking about the very problem addressed in this thread.

Take an example above.

Express A - - - - - - - - - F

Local A - B - C - D - E - F

And let's assume A is the largest city, while F is the second largest.

With the current loading system, convois serving the local services take passengers going to B, C, D, and E first and they carry passengers to F if there is any spare capacity, but they don't need to. Therefore, the number convois seving the local line can be minimal. And the convois serving the express line simply need to carry the leftover of the local services. And the number of the "leftover" is relatively stable.

But with your proposed loading system, local services will be likely to be filled up with passengers going to F first, because the number of passengers going to F is simply larger than that of passengers going to other destinations. This means the number of convois serving the local line will be surely larger than the above case to carry all the passengers to B - E. In addition, express route will become less profitable, since the number of "leftover" will fluctuate, depending on which passengers the preceding local convois load first.

In short, your proposal will be likely to reduce the utilisation rate of the convois.