In terms of ETH2, it is already quite profitable to mine ERGO or RVN or other proof-of-work GPU mineable coin algorithms (search for "what to mine" in your preferred search engine). The biggest question is, when ETH2 comes (whenever that is) will the profitability of ERGO and RVN increase or decrease with the influx of miners? Sure difficulty will spike massively, but in my opinion it is also likely that the value of these cryptocurrencies spike as well, however proportional.
The truth is no one really knows. I have an idea, but I could be wrong.