You definitely have to include the Dropbox sync function as realized in goodreader. this would be essential!
And I'm convinced a bunch of people will be willing to pay more for your app

Having a color eye dropper would be super helpful for color-coding info when highlighting or simply writing with a pen!
I also would like to have my custom colors saved such that any color I save on the app on my phone is saved so I can refer to it and use the same color when I use GoodNotes on my computer. Thanks!!

It would be really helpful for engineers and engineers to be if the ends of the lines would "lock" onto the corners of each square on squared paper.

That would make it a lot easier and faster to draw vectors, circuits, functions...

But only as an option that can be turned on or off easily like the lasso tool for selecting images or handwriting..., otherwise it would get very annoying.

Ability to recognize typed text and handwritten text in png or pdf when importing documents or handwritten notes in pdf from another application.

Would like to have more options regarding math figures.

LectureNotes does this very good (see attached image)

You can create and adjust coordinate systems, grids, dotted patterns, arrows, dotted lines and tables.

Add a paper page as new paper type with the date of today into the default paper type. So you are able to create a new note book with empty pages withe the date of today like a dairy book.

Should better and helpful if you can optimize to use ePub files

I wish there was an option for disabling the layering of the highlighter tool, since sometimes we need to colour diagrams or doodles and it gets impossible to do so with the highlighter because you have to do it correctly in only one stroke. If layering could be disabled, the highlighting would all be in one layer, and colouring in multiple strokes would be uniform and not look overlapped and irregular.

It should be allowed to show two pages of the same notebook at the same time instead of only able to show two notebooks side by side. This allows us to read more at a time, or even draw diagrams that can span two pages.

As a professional musician, GoodNotes is almost perfect for viewing and marking up sheet music both during rehearsals and performances! In my circle of friends and colleagues, GoodNotes is really becoming our go-to app! We unanimously agree that the only feature that is missing for viewing sheet music is the ability to view two pages at once (like an open book or in Mac's Preview "double-page viewing"). Is it possible that I'm just not seeing this feature?

Create simple hyperlink to other notebooks within a notebook.

Having the option of changing the whole notebook template with a simple click would be very useful for people who uses a lot of pages with grid template to standardize the writing at first, and wanting to change it to other template for a cleaner look.

It would be awesome adding some LaTex text recognition so Engineering or science students could be able to take amazing notes. Also increase shape recognition capabilities like Bézier curves. I ABSOLUTELY LOVE THIS APP!!!

Many users asked for a ruler but in my opinion it makes more sense to add a triangle ruler as a new funktion, because then you can't only measure lenghts, but also measure angles and draw straight.
Especially in math or physics classes, you often have to measure or draw angles.
And putting your physical triangle ruler on the iPad isn't a nice long-term solution, is it?
Therefore I would be happy about a triangle ruler funktion in GoodNotes 5 :D.

insert of split text function please... so if a user wants to add notes in between lines, s/he could insert a space and write

Currently I can only rearrange one page at a time.
If I want 5 pages to be moved up or down in page order, I have to rearrange one by one.

Have the option to add page numbers to the notebook pages. I sometimes need to reference a page of my notebook along with a task form another page or notebook, right now I don't see a way to have page numbers happen automatically when adding or deleting pages from the notebook. Having a link system (so my task says "see notes on page 4" and when I insert a new second page - the note is now on page 5, the text would change "see notes on page 5".)

Sometimes to sketch things out letter or DIN A4 are to short, so it would nice to have endless paper (like OneNote). Which you can scale if you need to print it out. Or have something like 4 DIN A4 papers which fit together with tesa strip.