So may there be the possibltly that some kind of extra reward can be send by the Algo to the miners by Scrypt or anything else with only a soft fork?
The difference between a hard fork and a soft fork is compatibility, and nothing more. A soft fork is generally preferred because it is compatible with previous consensus rules, and that helps avoid an unintended chain split.
The idea that the difference between the two limits which rules can be changed is misguided because, as Peter Tod demonstrated, pretty much anything can be changed with a soft fork.