Here in Ukraine we already have something like this.
There are licensed certificate centers which can issue certificates. Documents signed with them will be legally binding, with digital signature equal to personal signature (by law). For example, I use this to sign my tax returns. No special hardware is needed, though of course it's supported.
Of course, this can have privacy implications. However, it beats the hell of the stupid braindead SSN + birthday authentication scheme which is used in the USA now.