Yep, Navi will certainly be more Vega than Polaris in terms of its underlying architecture. It will certainly have DXR & DirectML support, as Vega is already well optimised for these workloads and Navi is likely to essentially be a gaming/consumer-orientated evolution of Vega, created primarily for the consoles(So no doubt MS has pushed AMD to make use of all these new APIs they've invested in creating, which is why DXR & DirectML support can't really be skipped.
Remember, DXR/RT is a cross-platform API led by MS and developed with all three GPU manufacturers in cohort (NVidia were just the first to attempt to push it to consumers).
The fact it's a mid-end architecture is mostly going to dictate how many CU's are on the dies, as opposed to what features it has. In this case mid range probably means just short of Vega in CU count but with more overall performance from IPC & clock gains.