Any speculation on this stems from them having just signed his backup for $25M/year as an extension off his rookie deal. Any team that trades for Highsmith would be acquiring him on a 2 years, $30M deal ($14.5M this year, $15.5M next year cash and cap for both, none guaranteed). Have to think he's going to want a new deal. But he's a super solid player at a premium position we aren't great at.
Landry was super solid before the knee injury last year but we don't know what recovery will look like and even at his best he still kind of struggles to win one on one. DJones is a good player but can also contribute inside too so more pass rushers frees him up to do that. Jacas is a rookie so always ideal to ease him in. And then guys like Ponder/Swinson have potential but neither have really proven much. So adding Highsmith to the top of the depth chart here would really allow everyone else to slot in to proper roles IMO.