We do have some stuff that ZenPayroll currently doesn't have such as the btc (which you mentioned) and our paycheck distribution which allows for employees to automatically take their paycheck into any number of bank accounts/bitcoin wallets.
RE integration: Yes. We realize that the taxes is a huge part. Currently we're offering a free month and plan to have tax deductions integrated before actually charging customers. You'll notice now, there isn't even a spot to enter your billing details for using the service. It's currently free.
The other stuff you mentioned is in our roadmap. We're just getting started and plan to add much more.