IMO, HomeKit support will add an additional method for remotely managing the Iro (that may or may not be more secure than the non-HomeKit method that the Iro has been using over the last four-plus years to communicate over the public Internet). I personally have no security concerns with how the Iro currently communicates over the public Internet.
But ... HomeKit doesn't support Android. Nor does HomeKit support web browsers running on computers.
Unless you're proposing that Rachio drop support for non-HomeKit devices (by only allowing HomeKit access), the Iro is going to have to keep the original non-HomeKit connectivity method that it's always had.
Adding HomeKit support to the Iro will be great (not sure it's a million-dollar feature), but AFAIK it shouldn't have any effect on the other methods the Iro retains in order to be compatible with non-Apple devices.