This is the flaw. The premises affirm the necessary condition of making the change (that the cost of the publication won’t increase), but this isn’t enough information to trigger the sufficient condition.

The editor does not comment on the reason that the journal is in a precarious financial situation. This is not an assumption that the editor makes. He only references the precarious financial situation to justify the conditions given for switching to an online version.

This possibility is irrelevant to the argument. Cost is the only metric discussed in this argument. Other advantages are beyond the scope of this argument.

The argument doesn’t need to rule out this possibility. The precarious financial situation is used to justify the claim that the change should only be made if costs won’t increase; it doesn’t t hurt the argument if the journal is still in a precarious financial position after the change.

The authority referenced is a treasurer and the treasurer is making claims about financial conditions. This is within the treasurer’s field of expertise.