You are confusing publishers with developers - though I can understand why, given that today most major developers are hand cuffed to a specific publisher.
id Tech seems to be landlocked to Bethesda based developers unfortunately, which is a shame as Raven used to be able to work magic with their engines. This is why id Tech is only found on Doom, Wolfenstein and Fallout now (Rage 2 uses something else).
As to RT and mGPU, in theory RT is already a highly parallel scalable compute problem - if you can do 1080p with one Vega 56, then 2-4 Navi cards should eat 4K for breakfast, even without FF ray traversal/intersection acceleration. The main problem in that is rasterising each frame, as even pure RT still needs to rasterise each frame to make it viewable, unless you are using a lightfield display that is.
Its worse than that. Even other Bethesda teams don't seem to be using it. They're sticking with their updated Gamebryo engine for Elder Scrolls and Fallout, nevermind how buggy it is (to the point its stopped being "charming" and is more they're shipping almost outright broken games with it with the last Fallout release). Its not like they can seriously argue against using idTech because it'd be buggy as their games are already buggy and seem to be getting worse in that regard.
Which, I get not forcing devs to have to us any certain game engine (I think that caused issues at EA when they were forcing Dice's engine onto everyone from RPGs to racing games), but I really don't get them sticking with buggy game engines over what seems to be one of the better engines.
There's little point speculating much only 2 days out, the Next Horizon disclosure on Zen 2 was heavy on details of the uArch - I'd expect the one on monday to do the same for Navi/RDNA, though the absolute nitty gritty will likely be saved for HotChips in August.
It gave some details but it didn't really tell us all that much. I doubt we even get that much info out of this event. We probably still won't get prices or real details. It'll just be "new arch, GDDR6, next gen!" type of hype. They'll probably demo it matching a 2070 again. And we'll get some token devs going "we've had a relationship with AMD for ___years, they're a great partner, we're soooo interested in the new architecture" type of nonsense.
I would really like to be proven wrong, but I'm not expecting anything but more vaguery (they'll talk up features - like how they talked up RapidPackedMath and stuff - that mean nothing to gamers because there's no way for gamers to actually be able to quantify any tangible improvement from that).
And that's why it doesn't even matter much, as it still comes down to the performance for the price. Its sounding more like I actually won't be upgrading from my RX480 for Navi, at least anytime soon if the pricing rumors are anywhere close to being true. As I doubt there's much fundamental changes (i.e. major performance improvement for the ~$250 market; no revolutionary feature - its not gonna come out and hammer RTX in ray-tracing even on the higher end versions, its not gonna have an Eyefinity bombshell, heck we'll probably just get some minor iterative improvement on the video processing block and video output - I won't even be surprised if AMD doesn't ship Navi with HDMI 2.1 ports; and even though I do think mGPU is part of the development that's going on with AMD GPUs, I'm doubtful we get anything related to that at Navi's release - although they might show mGPU scaling well in some specific game or something like they did with was it Vega?).