Just be aware that some users report save game corruption with the latest version of the SWP (4.3.2). I think there is a thread around here on GOG that links to the previous version (4.3.0) which doesn't have save game corruption.

Correct me if I'm wrong but indeed the SW source code was released too yes?
Why can't the devs behind EDuke implement it in their engine or make an EShadow?

Yes, the source code was released. http://www.3drealms.com/news/2005/04/shadow_warrior_12.html

No idea. I know that there is the SWP port and the JFShadowWarrior port, but it just seems like nobody else has tried to port it. :( Maybe, though, just maybe, the Steam version that has been released for free will get a port with the Duke 3D Megaton treatment. If that happens it should be possible to extract the port for use with any non-Steam version.

I'm aware of SWP, and frankly, I think it's shit :(
Don't get me wrong, it does what I want but still lacks features so simple that even EDuke prolly had it in their beta test.

both crash often on win7

4.3.2 does corrupt your save game files, not right away but over time they become inoperable. 4.3.0 is great if you just want to play single player or 1v1 multiplayer as it does not corrupt your save game files but I'm quite sure it only allows for only 1v1. 4.3.2 is good for multiplayer 1-8 players all day long. I also use win7. I use SWP 4.3.2 for single and muli however I dont really make any save games because I mostly just play user maps and also create maps with SWPbuild. It does crash the odd random time but it doesn't really bother me, I'm just happy to have a port.

I do hope this is awesome.