We will keep ZEO on a separate development track, then merge it into a future version of Zope. Note that this increases the need for Zope to handle ZClasses and Python Methods as first class citizens. Thus, ZEO allows all three tiers to be scaled and distributed in one facility. If you make a change to your logic, the change is distributed automatically to all sites on all networks. This is the beginning of the road for us to treat all three tiers as managed content.
Simplicity is a second major benefit.
ZEO is shockingly lightweight. Other facilities, certainly on Linux, require people to know an enormous amount about system administration. Yes, the Zope Storage Server then becomes a single point of failure. The next stage of ZEO will be to replicate the ZSS piece. However, since the role of the ZSS is so limited, the chance that it can fail are vastly diminished.