Iridient X-transformer produces a linear (demosaiced) DNG, that's its sole reason to exist, to do a better job at debayering than other software like Adobe. So it wouldn't make any sense for Iridient X-transformer to produce a mosaiced DNG because that would be basically a noop, the program wouldn't do anything.
So yes, of course that files produced by Iridient X-transformer are large, they are linear files. They are exactly three times as large because there are three color channels, four times as large if you also embed the original.
There is zero reason to convert RAF files to DNG files if you camera produces RAF files. The discussion we're having here is cameras producing mosaiced DNG natively, which as I hoped I showed you wouldn't come with any size penalty. The DNG can use modern lossless compression techniques, and can encode the same mosaiced (not debayered) data. And it works in every program, unlike RAF which always needs to be reverse engineered for every new camera release.
Also, I'm not confident to replace entire RAF collection with converted DNGs and delete originals.