Gapless over USB is never a problem. Gapless over ethernet often is.
For example, PS Audio's "Bridge" network streamer won't do gapless. They're working on a virtual soundcard to solve this issue but there are problems getting it finished. For a lot of people who enjoy classical music and prog rock the lack of gapless support with the "Bridge" makes it's network functionality relatively useless. In addition, the "virtual soundcard" software would still require a computer in order to stream over a network. This defeats the main benefit of network streaming. ie: streaming directly from a NAS without a computer.
As far as I know the only network streamers that can currently do this properly are the Linn DS streamers.
Luckily, according to Mike, the USB implementation on the Marantz apparently sounds as good as ethernet, so lack of gapless on ethernet wouldn't be a deal breaker. Hopefully, Marantz didn't overlook this important feature since streaming gapless over ethernet would be the main reason I would consider this DAC.
DSD over USB is a nice feature but only a fringe benefit due to limited content.
Terry