Disclaimer: This is purely my opinion, and is obviously quite speculative.
The damand for physical therapists remains high, as evidenced by the favorable job market. However, employers suffering from reduced reimbursement from many third party payors are going to continue to play things closer and closer to the vest, and this will likely slow down the acceleration of new graduates salaries. But in order to reamin competitive for new graduates I do think that salaries for new grads will go up, just not at the pace they have over the last 4-5 years.
Most employers will only have so much money they are willing to commit to staffing, and if they continue to have to gradually pay more to new graduates, they have to put the brakes on somewhere, and that will likely be at the top end of their pay scale. So, you'll likely continue to see the difference between what a new graduate makes and what a PT with 10 years of experience makes get smaller.
I think we are also much more likely to see salary be dependent on performance metrics, meaning the more revenue you generate for your clinic, the higher your year end raise will be. That way employers will be more comfortable paying an employee more, given the fact that the employee has a track record of generating more revenue for the company.