In 2014 I wrote a GPS software for my Jolla.
Due to QT-Location library not yet officially supported by SailfishOS (because in QT 5.1 it was still marked as "not yet stable API") I wasn't able to have it in JollaStore.
Year after year, Jolla conservatively kept QT 5.1 to not to wreck software compatibility.
In the meantime I continued enjoying my GPStuff even on Xperia X.

Well, four years later and after extensive testing SailfishOS eventually upgraded to QT 5.6 libraries: as soon as they release the updated Sailfish SDK for Lapuanjoki 2.1.4, I guess I'll finally see my four years old GPS app approved.
(and probably some old apps will not work anymore until updated).

Lapuanjoki features quite a lot of fixes, most notably SailfishX wifi hotspot.

There are still a dozen issues on Xperia X (sensors, carrier search, bluetooth, etc), mostly related to small things (for example, some users noticed in some case alarm didn't go off: here it's been months I use it almost daily, different alarms, and only once it didn't go off - I thought I just overslept).