Thanks Andrey, and just quick reply as what I was thinking when I created it and before I read your comments so replies are not arguing against.
There are AutoCAD .Net API by Autodesk® and Teigha .Net API Classic by ODA® exist.
I have never used Teghia or BrisCAD so never considered it but seen it mentioned many times and good points that need to be addressed.
Settings of the proj-files are to be independent of developer's computer.
Lib folder is for references and inside source control so no one should ever worry about where they are located or what version as it stays sync with source control, and ObjectSDK are only used to get a successful build. Did not want anyone to care or ever update, or even need to think where SDK is located as the files path are stored relative, also a accepted practice by many professional developers.
Unit tests are necessary.
I agree but did not know it was possible to do unit testing that would produce same results as AutoCAD or thought time it would take to mock or fake it and keep up with new versions it did not seem would be worth it, and have no idea about BrisCAD, Teghia, etc as never used it.
Don't create excess proj-files
2013 dll will work in 14, 15 , 16 but allows for system variable changes update to functionality and with shared project takes 10 minutes to create new project. and only what varies needs to be pulled out.
So up to developer to use just like referencing jquery, etc... can go back if wanted.
How do allow for updates or new functionality allowed for each year that gets a updated version each year?
Not sure how 2012 down would work with 2013 up with breaking change.
Will let comments soak in and post back later but thank you very much for great insight and ideas that I never thought of.