Our jurisdiction also needs to be able to enter a complete address and then be prompted with subaddress units without having to type out the first character of the unit. We fraction our addresses in an alphabetical way for certain locations (123 Main St., 123 Main St. A, 123 Main St. B, etc...) so the suggestion feature as it currently functions is unfortunately useless in providing suggestions for these addresses since you'd need to type out the first character in the unit name, which in our case would be equivalent to just typing out the entire address with the unit. We're hoping for someone to be able to type out 123 Main St. and be shown a list of 123 Main St., 123 Main St. B, 123 Main St C, etc. If they have to type as far as the first unit character then they'll never see any suggestions.
All attempts to create a single house - subaddress locator in catalog have shown very strange errors and "ghost" suggestions for addresses that don't exist. It adds on unit values for addresses that don't have any. I've been down the Gazetteer path but unfortunately some third party vendors use our locators and expect to see more information returned by a locator than a Gazetteer style provides.