I have done some works contacting some big NXT stakeholders to ask for supports for various NXT projects so far. It was a challenge. On the one hand, it is only right for big NXT stakeholders to contribute to build the ecosystem around NXT. A small contribution to NXT's ecosystem could increase NXT's value many folds and consequently increase the wealth of their NXT holding.
On the other hand, it could be unfair to ask only selected few big stakeholders every time. They have the right to ask "what about the others ?". There are still several big NXT holder still keeping themselves anonymous and the traditional method of contacting big stakeholders via their forum usernames is of no use in this case. These big stakeholders may want to contribute to useful project but they may not keep up with the most current development of NXT system.
Arbitrary message feature can help to eliminate this coordination issue since when the feature being implemented, a lead for a certain NXT project could send messages directly to top NXT accounts to ask for their supports. In this way, they will be all aware of the effort at the same time. A consensus could easier be built to support an useful project.
That's all for the benefit of a growing NXT network and its ecosystem.