Development on Ubuntu 17.10 "AA" has yet to officially begin with Mark Shuttleworth not yet announcing the codename. I've heard a yet to be substantiated comment from a fellow that part of the reason AA isn't yet open for development is they are weighing possible internal development changes, perhaps even making Ubuntu rolling-release-like, but not quite rolling like Arch or Gentoo, following the turnover and other changes going on at Canonical. Anyhow, the server team is moving ahead in trying to plan some of their work for the "AA" cycle.
At this week's server team meeting they mentioned their plans for shipping PHP 7.1 in Ubuntu 17.10 and PHP 7.2 in Ubuntu 18.04 LTS. PHP 7.1 has been available but didn't make it for Ubuntu 17.04 with PHP 7.0 being the default. PHP 7.2 should be available later in 2017 with a variety of changes.
For Ubuntu Server 17.10 they are also planning more dep8 testing. Other 17.10 server talk can be found via this Launchpad Blueprint. There are also this week's server team minutes.
Not mentioned is the reported new installer for Ubuntu Server. I'm excited to learn more and try out "Subiquity" but so far, no firm announcement. But presumably they will want their shiny new installer ready for Ubuntu 18.04 LTS, in which case they'll first want it in Ubuntu 17.10 for vetting, so presumably we'll see it premiere this cycle.
Stay tuned for more as Ubuntu 17.10 AA advances.