Hi Rick, curious if there has been any progress made on this in the recent Paint.NET builds? I've come across a 4:4:4 image that is beautiful, when edited and "saved" by Paint.NET it drops the quality down to 4:2:0 with no option to preserve the bits. It's a crazy complex image and the downgrade is quite noticeable. I've tried the OptiPNG-file-type-plugin but found that through several trials with different settings, the quality is preserved (awesome!) but the file size is not reduced relative to a standard PNG file.
Original File: 4:4:4 ~ 5mb
Save as JPG (100%): 4:2:0 ~ 3.5mb