What counts as use? Decoration? Easy fix, just slap a load of random stuff everywhere and it's done. Interacting with npcs or retainer bells? Easy, it's just one extra step after entering the house. Being in the house for a set amount of time? Easy, log in and go afk.
Using the workshop? What if the fc doesn't want to do that? Should a fc have to use a workshop to keep their house? Should a fc be forced to do something they may have no interest in, just to keep a house they may already use a lot but the game happens to not think they do?
There is no easy way to quantify use. It would have to be done on a case by case basis to not accidentally punish players who were using houses but happened to not be in a way software reads as use.
And honestly I don't like the idea of grading the use of houses as a way to see who deserves to keep a plot or not. This takes freedom away from players to use their house in the ways they wish.
14 days is crazy short. That would punish people for going on holiday somewhere without access to the game.
I understand that you're frustrated that houses you want are empty, but this isn't the way to fix it. The problem isn't the demolition timer. The problem lies in the amount of plots and SE not taking decisive action against house hoarders. There are some servers with wards owned by one or two people or a large number of shell fcs, which is ridiculous. SE also quietly lifted the restriction on fc house purchase (but did not update the lodestone entry about housing) and many are taking advantage of it, so that's not helping the situation either.
We will get more wards at some point with Ishgard housing, but if we don't see any action taken against house hoarders...it's just going to end up being the same situation in the end, again. There are probably people with shell fcs ready to buy plots there as soon as they become available.