Late last week, Steve Adams of MLBTR wrote about what an extension for Josh Harrison might look like. I'm a little surprised this has come up, because I hadn't even considered the possibility.
For teams, the main benefit of pre-free agency extensions is to control seasons they hadn't controlled before. I don't see that as a significant factor in Harrison's case. He's 27 and in the midst of an out-of-nowhere career season driven partially by a very high BABIP. He isn't a great bet to have a long peak, and the Pirates already control him through 2017. 2018 will be his age-30 season, and while there might be some benefit to controlling that year, the Pirates will have to balance that benefit against the possibility that he'll decline rather quickly, like a lot of guys who have out-of-nowhere career seasons in their late twenties. There's no reason for the Pirates to rush to control Harrison in 2018 or 2019.
They could, of course, sign Harrison to a shorter deal, perhaps three years (maybe with an option), to control his arbitration salaries. Such a deal would set Harrison up for life while ensuring that the Pirates keep his arbitration salaries low. The problem is that Harrison is already almost guaranteed a big chunk of that money -- he'll obviously be tendered a contract this year, which should get him $2.5 million or so, and he'd have to have a catastrophic injury for the Pirates to non-tender him for the 2016 season, in which he'll make even more.
At the same time, as Adams notes, Harrison's first arbitration-year salary will be dictated by his entire career record, not just this season, which should keep next year's salary relatively low. So the Pirates shouldn't be overly motivated to sign Harrison right now. If the two sides were to strike a deal, I could see something like three years and $14 million, or maybe four years and $22 million. But I doubt there will be a ton of motivation on either side to make that happen. Harrison's having an amazing season, but that in itself isn't a great reason to commit to him long term. He won't be leaving anytime soon anyway.