We already know the answer to those two. The new device will be based on the S905X4 SoC, which means it will offer hardware acceleration for AV1. See Will Vero Next have an optical audio port? - #40 by sam_nazarko and subsequent discussion.
Dolby Vision has also been discussed before in other threads - for example, Dolby Vision . The short version (as of the last time it was discussed) is that it will not be supported, for reasons that are legal rather than technical. DV has to be licensed by Dolby, and some of the restrictions on the system that they require to allow it would fundamentally destroy the open source nature of OSMC.
You can, of course, already play a DV UHD blu ray remux (DV profile 7) by simply playing the HDR10 layer and ignoring DV. There has been some discussion about the possibility of playing a single layer (DV profile 5) file by converting it to HDR10 on the fly - meaning it would play with correct colours, but without the dynamic HDR metadata. Don’t hold your breath for this; but last we heard it was still being looked into. If that does ever happen, I would guess it might be supported on the Vero 4K as well.
Sam is still being a bit cagey about that, but the stuff that we know about is mainly a somewhat more powerful CPU (which may possibly make general navigation a bit more snappy), faster built-in flash memory, one of the USB ports being USB 3.0 (which will be helpful if you want to attach a hard drive directly to the Vero), and the aforementioned support for AV1. Given the choice of SoC you should probably expect to be an evolution rather than a revolution.