Both formats seem extremely simplistic and I'm unsure if you'll be able to produce anything appealing if you try to import a map with those constraints. Unless I missed something you'll be unable to use 2 features of the DOS designer that look really important to me: texture blending and variable intensity.
I created the 3 images below to try to highlight those features:
http://imgur.com/a/ocvT7The first one shows that every tile of a DOS terrain can contain up to 20 different textures that are blended together to create more variation to the tiles. It's really important if you want to avoid repeating patterns but if I understood your wiki correctly, each tile of an L3DT map only has one texture. I fear that it'll make the map look monotonous to a human eye.
The 2nd and 3rd images show that, when a texture is applied to a tile, you can choose the strength of the brush applying it. Your L3DT spec seem to imply that texture presence is only binary in this format: the texture is either there or is not. In DOS editor you have 255 possible levels of intensity.
If I take the second image, that clearly has a low intensity texture in the top left area and apply a formula to force each tile to full texture or no texture, I get the third image.
As you can see, you still have the graphical shader that cuts the image smoothly around the stones but it remains very rough compared to the result that you could get with the DOS editor.
