What would you propose as an alternative?
The decision to amend the plan to allow for Roth is made above the participant level. If the plan is not amended, then the proposed participant communication seems appropriate.
Unless the financial institution has discretion to make plan decisions, including to amend plans to allow Roth contributions(or disallow catch-up), I don't see any alternative.
Plans are not required to offer Roth or disallow catch-up. Many the financial institution / recordkeeper do not charge enough or have a set-up that allows a lot of personalized customized plan design and follow-through, depending on the size of the plan. Unless they are on a service level where the financial institution is going to contact each affected plan sponsor personally, and educate them on the pros and cons of amending or not, I don't see it changing.
Does the financial institution also maintain the plan's document for these clients? If not, they really aren't in a position to do much else.
What is your role? If you are an advisor or TPA, those are the service providers I see doing more education with plan sponsors if a plan does not allow for Roth, but does allow for catch-up. I have had a number follow-up with sponsors throughout the year to educate and see if they would agree to plan amendments.