When I need to create a layout across a range of sizes, I place all the parts with spaces in between and use this option to export to .svg. (I turn off the labels and grainlines after the 1st one.) Then I import them all into the same Inkscape file. They all layer on top of each other perfectly and I can ungroup them and tweak their placements further.
Hmmm… Yes, when I found Seamly2D, I thought that all I needed to do was to put in my measurements and then choose the style I wanted. It was a huge surprise that I had to learn how to actually create a pattern 
However, there has been some talk, over the years, about the 3D mannikins and some people have imported their patterns into programs like MakeHuman or Marvelous Designer. There’s even a tutorial on Instructables on how to do this. But, for now, yes, our developers are very busy improving the program and I am so grateful to them, that I’m not even thinking of teasing them about this dream of mine 
Yes, this should be coming out soon. It has been discussed in one of the developers threads.
If I understood @Douglas correctly, he is busy with the idea of 3rd module included in Seamly2D that would be for grading and layouts to be sent directly for cutting in an industrial environment. Up until now, the software has been designed for very small/home industry and the bespoke fashion environment.
The idea has always been to help people to build up their fashion design businesses without having to spend hours and hours bent over a table drafting pattern after pattern by hand because patternmaking software is so very expensive.
As the program is now, I can attest to it that the software has definitely achieved this and more.