Well, there are already lots of LDraw parts available for after-market products, generally they are hosted on the website of these after-market product.
- Sbrick itself: https://www.sbrick.com/media/ldd/sbrick.zip
- Hitechnic sensors for NXT/EV3, Rotacaster omniwheels, Matrix metallic parts: https://www.hitechnic.com/downloadnew.php?category=23
- Firgelli linear actuators http://firgelli.com/Uploads/fla-v2.zip
...and some more here and there...
- Sbrick itself: https://www.sbrick.com/media/ldd/sbrick.zip
- Hitechnic sensors for NXT/EV3, Rotacaster omniwheels, Matrix metallic parts: https://www.hitechnic.com/downloadnew.php?category=23
- Firgelli linear actuators http://firgelli.com/Uploads/fla-v2.zip
...and some more here and there...