As a red teamer developing malware for my team to evade EDR solutions we come across, I can tell you that EDR systems are essential. The phrase "root kit powered endpoint surveillance" is a mischaracterization, often fueled by misconceptions from the gaming community. These tools provide essential protection against sophisticated threats, and they catch them. Without them, my job would be 90% easier when doing a test where Windows boxes are included.
> So the main tool would be open source and it would be transparent what it does exactly and that it is free of backdoors or really bad bugs.
Open-source EDR solutions, like OpenEDR [1], exist but are outdated and offer poor telemetry. Assembling various GitHub POCs that exist for production EDR is impractical and insecure.
The EDR sensor itself becomes the targeted thing. As a threat actor, the EDR is the only thing in your way most of the time. Open sourcing them increases the risk of attackers contributing malicious code to slow down development or introduce vulnerabilities. It becomes a nightmare for development, as you can't be sure who is on the other side of the pull request. TAs will do everything to slow down the development of a security sensor. It is a very adversarial atmosphere.
> On the other hand it could still be a business model to supply malware signatures as a security team feeding this system.
It is actually the other way around. Open-source malware heuristic rules do exist, such as Elastic Security's detection rules [2]. Elastic also provides EDR solutions that include kernel drivers and is, in my experience, the harder one to bypass. Again, please make an EDR without drivers for Windows, it makes my job easier.
> *It could be audited by the public."
The EDR sensors already do get "audited" by security researchers and the threat actors themselves. Reverse engineering and debugging the EDR sensors to spot weaknesses that can be "abused." If I spot things like the EDR just plainly accepting kernel mode shellcode and executing it, I will, of course, publicly disclose that. EDR sensors are under a lot of scrutiny.
[1] https://github.com/ComodoSecurity/openedr [2] https://github.com/elastic/detection-rules