One of the motherboards on display at the MSI booth was an updated AM4 socket Tomahawk series board that uses the new AMD B450 chipset. The MSI B450 Tomahawk is a refreshed motherboard for AMD Ryzen processors. The motherboard pairs the AM4 socket with four DDR4 DIMM slots, six SATA 6 Gbps ports, two PCI-E x16 slots, three PCI-E x1 slots, and a single M.2 slot.
The B450 Tomahawk is powered by an 8-pin and 24-pin power connector and appears to have a 4+2 power phase design which matches that of the current B350 Tomahawk. One thing that MSI has changed in that department is the heatsink over the VRMs which has been beefed with an "extended heatsink design" that up an extends to partially cover the rear I/O ports now. Other updates versus the B350 Tomahawk include the removal of two legacy PCI slots in favor of adding a third PCI-E x1 slot and the addition of two additional SATA ports in the lower left corner.
It is not clear what the board specifically has as far as rear I/O, but from the photos and press release it appears as though the VGA port may have been removed versus the previous generation board and it does have USB 3.1 Gen 2 along with Gigabit Ethernet and analog audio outputs (looking at the photos the audio hardware has slightly changed as well though it's hard to say to what extent).
MSI is not yet talking pricing or availability, but more information should be available soon. TechPowerUp has a hands on photo of the board here as well as a cheaper and cut down B450-A Pro motherboard.