It is very interesting philosophical question ). No one can say for sure what would be the BTC price and market dominance even in a month. And price prediction for long term is million times harder then for short term.
But I also have a guess ). I think that after some point, for example when BTC price will be near to $3000, the dominance of BTC will be about 90%. And after that we will see a gradual and constant market growth and reducing dominance of BTC to current value. Of course, there will be local falls and ups, but in general it will be slow but steady growth with an increase in the weight of altcoins.