Intel published a paper giving an overview of the features to expect on motherboards using Z390 chipset.  Most of the features will be familiar so why not start with the fancy layout diagram?

One of the features you might not consider, but perhaps should, is the combination of the quality of the onboard graphics chip on Coffee Lake with the outputs of a Z390 motherboard.  The motherboard can support up to three HDMI or DP outputs, which can provide 10bit colour, High Dynamic Range and Rec. 2020 at up to 4k resolutions.

Storage options are as you would expect, with Intel Rapid Storage Technology supported for both SATA and PCIe, with support for Optane if you so choose to use it.  Intel have updated their HD Audio in this generation and their Smart Sound Technology branding indicates the presence of a DAC on your motherboard. 

Networking is also worth a mention, with gigabit transfers available on the integrated NIC as well as through the Wireless-AC 9560 NIC, with integrated Bluetooth 5 support as well.  

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Yes, it will support overclocking unlocked processors.  The PR is below.

CREATE YOUR NEXT GREAT PERFORMANCE WITH THE 8TH GENERATION INTEL CORE PROCESSOR
The Intel Z390 chipset and 8th Generation Intel Core processors give you the edge you need to successfully defeat your rivals. Quickly upload and access your favorite streams and get the gaming boost you need with Intel Turbo Boost Technology 2.0 and Intel Hyper-Threading Technology. With the Intel Z390 chipset and 8th Generation Intel Core processors, you can conquer your quests with confidence.

GREAT PERFORMANCE – UNLEASHED
Release your inner gaming beast with the Intel Z390 chipset and unlocked 8th Generation Intel Core processors. Unlock your core, graphics, and memory frequencies to new levels as you defeat your gaming foes. Gaming and productivity is redefined with the Intel Z390 chipset paired with new unlocked 8th Generation Intel Core processors. Crush your competition with 8th Generation Intel Core desktop processors and the Intel Z390 chipset.

FAST PC RESPONSIVENESS AT YOUR COMMAND
The Intel Z390 chipset and 8th Generation Intel Core processors enable support for Intel Optane memory which speeds up access to your favorite programs and files. With the fast application response times enabled by Intel Optane memory, you can quickly access your digital life. Experience immersive sound quality via Intel High Definition Audio and enable your PC to respond to your voice commands with Intel Smart Sound Technology.

UNLEASH YOUR NETWORK PERFORMANCE
Achieve Gigabit wireless connections with 1st generation integrated Intel Wireless-AC support. The Intel Z390 chipset integrates an Intel wireless 802.11ac and Bluetooth 5 solution allowing you to connect up to Gigabit Wi-Fi speeds with Intel Wireless-AC 9560. With no Ethernet cable required, your desktop will be ready for all current and future wireless use cases and has the flexibility to be located in more places within your home or office.

IMMERSIVE VISUALS WITH INTEL UHD GRAPHICS
Intel UHD Graphics on 8th Generation Intel Core processors provide eye-popping 4K UHD resolutions. Experience more immersive gaming with High Dynamic Range (HDR) and Rec. 2020 (Wide Color Gamut) support. Playback your favorite videos with color precision via native true 10-bit graphics output. Watch the latest 4K UHD premium content on your PC from leading online providers. With up to three independent, DisplayPort* and/or HDMI* displays supported with the Intel Z390 chipset, you can immerse yourself into your gaming experience.

MASSIVE STORAGE CAPABILITIES
Expand your storage capabilities with the Intel Z390 chipset and 8th Generation Intel Core processors. Boost your media transfer speeds with the integrated USB 3.1 Gen 2 support of the Intel Z390 chipset. Create fast storage volumes and back-up your media and critical information via RAID support with Intel processor and chipset-connected PCI Express* SSDs. Expand your storage with up to 6 SATA 6 Gb/s ports. Enable blazingly fast data transfers to your favorite devices with PCI Express* 3.0.