On the topic of using off-brand parts in MOCs- if you are just building something for yourself, of course anything goes. But when it comes to (LEGO) online communities, it's a different story. The whole reason why certain MOCs are considered brilliant and why "NPU" exists is because we are all working from the same limited pool of parts (which gets increased yearly by the LEGO Company) and often times a new build or technique is impressive exactly because the creator managed to find a new, previously unseen combination from that limited pool of parts. I believe a lof of the hype around MOCs comes exactly from this, and it's also why websites like The New Elementary exist in the first place.
Once you introduce off-brand parts to that... Well, it's the Wild West then! Of course, it automatically makes many, many more things possible (I genuinely cannot understand why LEGO is refusing to introduce certian bracket pieces) but at the same time removing those restrictions makes many things less impressive... You see someone's new MOC, you wonder how they constructed something- it turns out that they used a random part from a random alternate brand which is not even available in your country. Great!
So personally, I am not for mixing parts in MOCs, or at least not in MOCs that you post online. In my own collection, I will always keep other brands separate from LEGO. But going back to the main question of the thread... I do believe the alternate brands deserve their section (or sections) on this forum. Firstly because many of them are genuine, quality products and they deserve addtional exposure and more places online where their products can be discussed. Secondly because I feel LEGO has lost its touch (and whimsy) and I believe it would aslo benefit them to read and see how AFOLs feel about alternate brand sets, and what those brands are doing right. And thirdly because well, I personally want to have a placce to discuss those sets.