No. There is no reason then to play an Int based assassin if Dex becomes an option for Assassinate DC. It is easier to get your Dex higher and it doesn't require the huge investment of AP into Harper for Int to hit/damage. Concerns about not enough skill points are also completely invalid, unless you then dump Int but in that case it is your choice.
This would kill off Int builds except for flavour, and Int makes the class more challenging and fun as opposed to Dex.
Though I think Dex could be applied to Shadow Dagger DC, it is a lacklustre enough ability, let it get more use from Dex builds too since that won't really effect the class overall.