@christianclavet,
Thanks for a very detailed and easy to follow request. I'll definitely be taking these suggestions on board.
deepMesh already has CSG tools similar to valve's hammer editor, although this isn't the main way of modelling in dM - the option is there. I'll look into improving the workflow for this way of modelling (see the CSG section of the manual).
Also, the tilable textures feature in hammer is already in deepMesh. The option is available from the 'Materials' tab, by clicking 'Paint Mode', selecting 'paint triangles' and clicking the 'Auto-map' button near the bottom. This is another area which could benefit from easier workflow - will add to the list.
I guess what deepMesh needs more than anything is a set of decent tutorials, since many of the features are hidden away. There are plans for a new manual, tutorials and videos etc.. but this is very time consuming.
Here's a map I'm making in deepMesh v1.3c at the moment, which was built by subtracting cubes (cuboid split tool), reshaping, adding details, painting textures and lightmapping - all done in the editor. The shaders were added in-code...
Not especially impressive, but I'm a coder, not an artist.