Hold-Spacebar to move cursor: Simulate vertical cursor movement workaround suggestion.
The addition of hold-and-slide on the spacebar has been great. I know Apple has restricted vertical cursor movement.
A workaround suggestion: I don't know if Apple permits it, but
I suggest that if upwards/downwards movement is detected, the cursor moves back/forwards approximately the number of characters in a line, (say about 40 or 50 characters), until you release your finger. It doesn't really matter if it doesn't end up exactly above where it was, all we need is to go backwards in our document quickly!
I know there's not much space for downward movement, but there's a few mm, and perhaps if we slide down a few mm and hold, the cursor could keep moving to the right by approx 40 or so characters per each 0.2 second (or so) until you release your finger. Likewise behaviour would occur when you reach the upward limit of movement.
It would also be nice if when we hold the shift key whilst doing this, it selected the text. It's been mentioned in another suggestion somewhere I think.

Sorry I forgot to update this but this was implemented in Typefinity (not PadKeys) a while ago.
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F Hiew commented
Hi, good to hear from you guys again: great job on that! I enjoy being part of the input process and seeing The keyboard being improved! :)
I just bought Typefinity and checked it out. A few comments (iPhone version):
1. It scrolls at about the right speed. :)
2. Vertical sensitivity is perfect when using the notes app.
3. Vertical sensitivity when typing in this comments text box on this website is a little too hyper-sensitive: I have accidentally scrolled upwards a few times when trying to move the cursor to the left, but this may be to do with the website's or Safari's behaviour.
4. I think that with downwards movement, the cursor should continually keep moving downwards when you hold your finger in the "down" position towards the bottom ~2mm of the spacebar (after a short delay of course!).
That would help with long documents, and put Typefinity ahead of the Apple keyboard in that department!5. It would also be good if the same behaviour happened with upwards scrolling, when you hit the top ~2mm of the screen.
6, Lastly, it also would be wonderful if holding down Shift and/or Option while doing this would select the text as you drag. (Shift-drag would be the same as the standard Apple keyboard, closer to a computer keyboard's Shift+Arrow behaviour; Option-drag feels a bit more intuitive to me, as it's in the corner and on the same row as the space bar, but either would do (I recommend having both combinations active). This would enable copying-and-pasting an entire paragraph easily.
Again, great work! :)