There will be bigger adoption of blockchain technology and cryptocurrency so consequently there will be more thousands of altcoins to be created in future. Will the balance between Bitcoin (only one cryptocurrency) and thousands or hundred thousands of altcoins change?

I believe it will be changed in market cap dominances as it has already been changed since 2009 and appearances of what's called as alternate cryptocurrencies. However, it's tip of iceberg and it can not hide a big fact that Bitcoin dominates this market even its dominance drops with time. Bitcoin dominance drop does not mean it loses its big role in this market, but it is because there are more and more scam altcoins created with time and those scam altcoins contribute more fake marketcap to altcoin ecosystems.

At the end, altcoins die mostly but more severe deaths in bear market which is when you see Bitcoin dominance stronger and clearer.
https://coinmarketcap.com/charts/bitcoin-dominance/