This I meant, use SegWit transactions for low valued transactions only, because they meant to be as anyone can spend and the signature is required only in withness data by certain block versions,
They are not meant as anyonecanspend outputs after the activation because they aren't anyonecanspend outputs after segwit activates.
I understand this, these SegWit transactions are meant as anyonecanspend outputs after the de-activation, the same way as today. The only thing what protects SegWit transactions from anyonecanspend after activation is just another Soft fork which deactivates use of withness part to check signatures, users should be well aware of this and act accordingly.
but this signature in withness data requiremet can be changed with future soft fork and new block version again.
Literally anything can be changed with any kind of fork. This is not a valid argument.
No, you can not spend normal transaction after any Soft fork without valid signature, but you can spend SegWit transaction without signature afer Soft fork, so "Literally anything can be changed with any kind of fork" is invalid statement.