1)Detail work on a proven, existing platform,working from an established knowledge base and aftermarket sources. An AC benajmin with a skeleton valve would fall in this category.
2) Come up with a combination of parts currently available, but combined differently than anything on the market..a Benjamin pump tube plumbed to a Disco would fit in here, or a QB with a 1400 pump built in.
Both the above have the advantage of being possible to assemble in a typical home shop, if you have cooperative aftermarket suppliers.
The third approach is much less modder friendly.That would be..
3)Scratch built, blank slate design. The vertical valve hammer gun I mention lower on the page is in this category, as are the couple guns that I know Ron has built...there are very few here on the green that have the skills and the shop to pull off this approach.
It strikes me that we need to pick an approach, just to narrow things down a bit.
Can we acknowledge that batteries aren't to the point that we can power on board electric compressors, and let that idea go?
Give me 8 months to get situated out East and purchase some real machine tools, it's on. I'll build either a one off system, or build one that uses current pieces parts...
Honestly can't figure out why some of the tool owning folks have not built one up.

"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."