Satoshi had already thought of the quantum computers, and the possible decoding of the privatekeys if it became available, but I think, Satoshi as a programmer, he know that Bitcoin security will not stop developing and improving so he do not worry much about this stuff.

I do not know why people think that Bitcoin security will stop as is and too worried about quantum computers.  It maybe a threat but I am sure, Bitcoin developers will find way to level Bitcoin's security up before that happen.