I forgot to add this to my last response: If one has a synch broadcast implementation, why can't one implement the "all-you-can-eat" calculus by the dualizing translation where every send becomes a receive and every receive becomes a send? Is there some asymmetry in your notion of observation that this translation is not meaning preserving?
my application makes input and output asymmetric in a way that precludes this dualising translation (output subjects vary with time). i suspect that this would also be the case for the leadership election outlined by pawel, because values are being passed. however, for pure "all-you-can-eat" synchronisation, your suggestion seems to work.