Hi Jaahan,
I don’t have experience paddling with a dog, but I think your comfort will have as much to do with your dog’s temperament and the distances you plan to paddle as anything else… I have paddled at a leisurely page with two people in a Small size DIY Packraft for an hour and that was fine in regard to buoyancy, handling, and comfort – in fact, that extra weight improves handling by reducing yaw. In general, I think paddling with a dog would be more to the “mildly off-putting” end of the spectrum. For safety’s sake, I would avoid unpredictable whitewater though!
I’ve stopped giving ETAs on new plans, as they always seem to take longer to develop than I anticipate. If people want a stretched version of the Large packraft, I can make that pretty easily, but it’s not going to be the ideal 2-person boat because it will have the same characteristics as the other extra-long packrafts that are commercially available (flexible and floppy).