I could easily see Arrieta coming to Philadelphia, this smells an awful lot like Werth to the Nationals 7 years ago. Boras understood that while the Nats were seen as terrible back in 2010, they A] had a strong young base of talent, B] lots of money to spend and C] an owner who wanted to get his team relevant again. This sure sounds like the Phillies circa 2018 to me.
Boras also knows that the Phils are likely to be "in" on Harper after the 2018 season and this would be a good time to establish a relationship with a team he has historically turned his back on. I also found it interesting that in today's ESPN MLB Insider story [couldn't read it] the Phillies were the topic of a story about teams that seemingly are on the outside looking in but well could contend this coming season. I believe it was probably written by Buster Olney, a guy often connected to Boras [as is Heyman.]
I could well be wrong but my sense is that the Phils right now would prefer to sign a FA pitcher than surrender their young talent for pitchers that arguably are not that much better than the potentials of some of the guys they already have.
The signing of Santana showed me that the rebuilding days are over, they are quietly convinced that with the proper moves they can contend. I agree. I also believe that if they do sign Arrieta as a FA, they may revisit the Machado talks as they well may have a couple of young rotation pitchers that the Orioles like and from what I have been reading in the Baltimore papers, the O's are convinced they have to move Machado before ST regardless of what they are saying publicly.
With a young core, Santana and Arrieta in tow, and tons of money to spend the Phils well could allow him to get comfortable this year with the belief that A] he will like it in Philadelphia and like what he sees, and B] honestly there are maybe 2-3 teams, Phillies included, who could pay MM north of $300 million next year and still stay under the luxury tax.