1/ "Once 95% is reached" arf arf arf you go first.
2/ Validation? like in accepting segwitted transactions? hoohohohoho..
I will gladly upgrade and you can stay on your old implementation and pay a higher fee than me , thus it is backwards compatible.... but be advised to wait for confirmations on segwit tx's as your old wallet will have degraded security with regards to those tx's.
Will you be creating an implementation to reject segwit tx that are even confirmed?