Allright, it has been solved now!

Thousand thanks to @sledges & @pketo who fixed it; now my Nexus5 sees all the applications in the store!

How it happened; it seems that the store has already been open for all ported Nexus4, Nexus5 and Fairphone2 devices, however when the store backend was updated some time ago there was a regression that blocked the Nexus5 devices off. Now that bug in configuration has been resolved and Nexus5 users can access Harbour again.