The fallow period sounds waaaay to short. I suggest 2 months at minimum
since anyone that wants to be safe needs to upgrade.
I asked a lot of businesses and individuals how long it would take them to upgrade to a new release over the last year or two.
Nobody said it would take them more than two weeks.
If somebody is running their own validation code... then we should assume they're sophisticated enough to figure out how to mitigate any risks associated with segwit activation on their own.