This may be the beginning of the end for the 744s, but more immediately will provide a path for phasing out the older 772s. UA was the launch customer for the type. With an average lifespan of about 25 years on an airframe(Yes, I know we actually count cycles but work with me here), some of those first planes are about due for their trip to VCV.
If we're not going to be flying 744s on routes like SFO<->SYD anymore, I'd like to see the 772s currently doing those trips replaced w/ these new 773s.
(Although given the choice, I'm sure SMI/J would just as soon bring back the DC-6).