Thank you for the relative coordinate feature. I will try it later.
Adding more polar setup angles is okay but not necessary, you should consider to allow users to type the degree directly when using the command. (I am a teacher too), I saw students prefers using mouse and click more often but I know many serious users they prefer by typing it when using CAD. Able to use keyboard for provide both the relative coordinate and the polar angle degree are great, it's really make you work fast.
For examples:
@30,20 ---> relative coordinate +20 for x and +30 for y
@30<20 ---> relative polar angle length 30 with angle 20 degree
I understand pdf export and printing are hard to implement features. I wish I can help you but my programming skills still aren't good enough for that level.
I understand you said that grid is the past. Not sure how about the others, but I use grid for visual purpose only, not for snapping. For example when I am drawing a floor plan, visually it looks good if I put a table there. But I need to know the distance between the table and the wall (without using dimension tool to measure it). I simply see that there are 8 dots between them, it means it is roughly 90cm. Very useful, isn't it?
Thank you for your attention. ZCAD really is a great program but it is not good enough for serious architectural drawing. Actually I ever tried ZCAD long time ago, I searched and tried (I believe) all the AutoCAD alternatives that can run on Linux including ZCAD. Hopefully, not long later ZCAD already has all the essential features and I can use it.