I have no idea what is happening with evening dress aboard MV Golden Princess or, for that matter, what will happen when she comes to the Caribbean in a couple months.
To date, I have yet to see anything official from Princess about any elimination of semiformal evenings. I have seen a couple posts on this board indicating that some cruises aboard MV Grand Princess did not have semiformal evenings in the Caribbean (the affected cruises reportedly had two "formal" evenings and five "casual" evenings), but it also is not at all clear that this is in any way tied to the "Personal Choice Dining" program. Additionally, MV Sun Princess, MV Dawn Princess, MV Sea Princess, and MV Ocean Princess were to implement the "Personal Choice Dining" program upon arrival in Alaska last May -- and I have not seen any posts indicating that any of those vessels have eliminated semiformal evenings, either.
As best I can tell, the reported elimination of semiformal evenings on at least some sailings aboard MV Grand Princess appears to be a local decision of that vessel's staff rather than a matter of corporate policy. Thus far, it does not extend to the rest of the Princess fleet. Also, there's no basis to be certain that it's a permanent arrangement aboard MV Grand Princess.
My recommendation is to "Be Prepared" -- just like a good boy scout -- for a couple semiformal evenings on a seven day cruise.