Moreover, in my opinion tech questions about designing systems in a non-vendor predicted way should be valid as long as they cover a valid business need. It seems that to a lot of members, using a setup not offered by presales is not a valid question.
I disagree with that.
- Serverfault is a Q&A site and should provide answers to common problems based on a good foundation.
Working in unsupported environments generates enough individual problems that the majority of professionals would never encounter.
- It's members are all voluntary with limited time. They are here, because they not only want to help, but to improve their own skills and learn a thing or two. Hence Serverfault relies on the precondition, that the questioneer exhausted all possibilities to fix the problem on his own.
If we allow questions about problems in unsupported environments, Serverfault may get flooded with questions, that won't be answered. This may lead to less traffic because nobody is interested in sites where there is a big chance that a question won't be answered, or there is no solution to ones problem.
A question based on an unsupported environment won't attract as many people to help, because what you learn will probably never apply to a professional working in supported environments. If you learn anything at all.
Above all, who would like to spend his time to figure out a problem, that could have been avoided in the first place? In many, many cases it would have been cheaper, to just invest in a supported environment.