My real concern for RTG is that Volta will be the death blow.
Although it won't be a death blow per say, its going really limit AMD's market share growth in dGPU markets, all of them, from HPC, DL (which are non existent right now), all the way to consumer. AMD needs to be competitive pretty much in the performance market and down if they don't' want to see their market share slip any further. Will Vega 11, 12 be able to compete with Volta's mid range? We already know what will happen in the performance segments, that is a forgone conclusion. Dual GPU Vega will NOT compete against these cards, it can't even compete against Pascal.
If AMD is able to do something similar with Vega 11 and 12 as they did with Polaris 10, they might be able to stem off the market share bleeding, but I think that is a tough call to answer with what we know about Volta and what we see with Vega currently. They have to get oh at least 60% better in perf/watt to match Vega in the mid range, probably closer to 100%, at 60% increase they will match Pascal's performance segment, which Volta's mid range should be around Pascal's performance segment in performance and factoring in lower power consumption, yeah 100% seems likely is what Vega 11 and 12 have to reach to match Volta.