“If you need to do it we can draw it in 3D” 
I understand that there are no curves in SketchUp, but I use a plugin that does the emulation. I’d like to have that in the native tools.
This seems like a good opportunity for you to create a SketchUp competitor, with all the better features, and sell for it for a reasonable price. SketchUp will price themselves out of the market and your product will be going strong.
I wonder if you can get AI to look at SketchUp and it’s program, and create something similar…
AI cannot generate a program of this complexity on its own. However, it is a huge help, making it possible—given time and a lot of hard work.
There is no “polyline” tool, though the concept exists internally—specifically for handling arcs, which are essentially groups of line segments with arc properties. In fact, you can group not only arcs but also straight lines to create a continuous path. While not particularly useful, it is possible to do this by selecting the lines and right-clicking to choose “Weld.”
Furthermore, you seem to be unaware of many SketchUp tricks, and you do not appear to fully grasp the nature of the software.
I agree with you that SketchUp should be sufficient without plug-ins, and for me, it practically is. As I see it, the problem lies elsewhere.
Furthermore, you seem to be unaware of many SketchUp tricks, and you do not appear to fully grasp the nature of the software.
Actually I’m very aware of many, if not all, SketchUp tricks, and, were I to be tested, I would be found to fully grasp the nature of the software … Pro that is.
For example, there are various ways to cut solids.
And if you need this capability regularly, that’s where a plugin comes in handy—to boost productivity. Most users don’t need it, and if they do need it once, they’ll find a way to do it using standard tools.
I’m very aware of many, if not all, SketchUp tricks
So humble
That’s great. With that level of SketchUp knowledge, you might enjoy expanding into other 3D tools as well, like Blender or Unreal Engine, if you haven’t already. There’s always another level to explore.
As a professional designer who has used AutoCAD for over 35 years, and SketchUp since 2013. AutoCAD has model space (design), and paper space (documentation). SketchUp has SketchUp (design), and LayOut (documentation). No matter what the design is, from a piece of equipment to multiple story building, clients don’t pay unless they get documents, nothing gets built without documents.
Some users simply need a design tool that offers a visual design without documentation other than a printout of the design. To that I recommend the free version of any typical cad program. If they need more developed (tools) to complete the design, then any paid version is providing the tools, even if one of those tools include documentation. It’s unrealistic to ask for more and then complain about what “more” includes.