I saw some posts about DAG file on ethereum and it influencing AMD cards (all rx cards the most).
apparently they don't seem to have a bright future, can amd driver updates more or less fix it or is that already taken into account?
or is in a year or so time the only way out mining a different currency like Zcash and for those it seems that nvidia GPUs are just much better?
As long as the profitibility is there with cryptonight algo, AMD cards are going to kick ass. If that changes, they might not kick ass as much. That isn't to say your AMD rig will be useless though.
The fact that AMD Vega's have been so hard to find has forced me to buy Nvidia gpu's and I think that's a good thing. Diversify your farm.