Let people post piece ideas
Mark Bellis commented
This would have to be a separate site because there are so many ideas out there. I have suggested about 50 pieces over the years and even made a few from spare parts myself. You can make a LEGO lathe to "turn" items with an axle on a fast LEGO motor. I don't do it with parts from sets though.
I have no doubt that the company has tried most of the things I would suggest. They will have drawers full of prototype pieces that have never made it into a set.
One thing I would like is, despite all the arty pieces these days, completion of the ranges of size of core technical pieces. Some Technic builds are convoluted and could be made simpler with brackets like a musical "minim" shape.
I vote for this, too! Too bad it may never happen because LEGO Ideas cannot allow their users to include new-mold parts in product ideas. However, I have seen "new parts" such as that cloth piece covering Fred Flintstone's car! Who knows?