Turbotax does not allow addition or substitution of forms or PDF files. Some other tax programs do allow attachment of PDFs, but I don't think that will fix your problem, since the PDF attachment to the XML data file is not going to be part of the e-file validation.
What's supposed to happen is you e-file your return with the electronic form 8283, and Turbotax prints out a transmittal form 8453, that you mail to the IRS with the original copy of the 8283 signed in ink. I don't know of a change that would cause the IRS to reject a return without a PDF attachment. You may want to call customer service and see if you can get an application specialist to review this.
