The average residential panel is generally so lightly loaded at any one time that I don't see it as much of a safety issue. The load on the bus is only going to change by the amount of additional things put on it.
You could put 20 subpanels in a 40 circuit panel, and not increase the load at all.
Eagle, is there a reason that you can't increase the # to 42 anyway??
Commercial work could be a completely different story, however.
