the bottom line is that forking the blockchain is costly and requires a lot of organisation at present, so we aren't going to see forks adopted that only contain small changes. this means that forks have to be collections of changes that often include larger work/changes. this in turn means that only really the main development team are likely to ever release a fork that gets accepted. the best option currently for getting a change like this implemented is for it to gain acceptance with the wider community without actually coding it, then having it included in a future fork.

changes like your proposed one aren't something that can really be tested other than on the live network because their implications are more social/political and take more time to manifest than testing usually allows.

the idea itself is interesting to me, however, it does imply that rather than having a 'tyranny of stake', we might see a 'tyranny of habituation'.. In other words, great people might get zeroed out just because they had to leave the blockchain for a while - whereas the anti social people might gain power just because they keep posting. In fact, it would motivate the use of bots to keep accounts active, which would not be healthy for spam on the network.