Yes, the programming and maintenance of code is quite an issue. I do not know anything about Carlson's code base.
I do know the Intellicad lisp performance is below Bricscad's lisp performance and Bricscad lisp engine is much more code compatible to Autocad than Intellicad is. Bricscad lisp includes most of the visual lisp function Autocad has. Also, every incompatibility I have bumped into between Autocad and Bricscad lisp has been resolved with urgency.
If Carlson is developing in C++ using ARX on Autocad and Intellicad is based on the ODA libraries and SDK there are two very different code sets to maintain. Bricscad has been in the process of wrapping the ODA libraries to create their BRX SDK which is designed to make it much easier to port their Autocad ARX code to Bricscad BRX with minimal changes in code and functionality. The BRX library has been improving by leaps and bounds with each annual update.
As for the .Net, Bricscad has does have minimal support currently and will also be expanded rapidly. The API is again intended to remain code compatible with Autocad .Net.
Bricsys is very responsive to fixing reported bugs. Often within a week or two there is a public release to fix the issue.
I have nothing against Intellicad products. We have had them here in some form or another for 10 years and I agree the Intellicad platform has improved significantly in that time. It is just moving soooo slow in a manner that seems to me will require Carlson to develop and maintain two code bases so the two will not have the same functionality.
Well, hopefully the Intellicad consortium has developed this v7 code base so it is clean and flexible so it can progress rapidly in a stable manner like they are saying in the new releases. I have been trying to remain patient but it is hard! Sorry