Not a bad thing to have. Unlike in real world, we can't step away from the canvas (well, we can, but it gets too small). Sometimes I use Apple TV to view it on the big screen, but it's not convenient during the work. Even having a thumbnail is important for overall composition.

3- and 2-point perspective guides would be super helpful.

Super! So, using Wacom with one hand and touchpad with another is not a problem?

Don't forget to mention the Dynamics and colorize each stroke. The feature is tricky. I still haven't figured out their use of it, except for using it almost like a wash brush - smear doesn't do stood job of it, only in very low flow settings. Problem is that the app doesn't have a "background" (or second) color in eyedropper settings. Without that you'll have to go and edit brush every time you need to change the mixture color. It has to be more dynamic. Plus it needs to be also mixed to transparency.

For a decent size giclee print one needs at least 8000 px artwork (ideally it should be much bigger). How many layers can a file have on iPad before it slows to a crawl? Screen resolutions of course may have more layers. 4K screens are the reality (and not very expensive). 8K will be available soon.

It's default because it's the easiest and fastest (except for "none" of course), not because it produces the best results, especially when it comes to the art.

"None (nearest-neighbor): Use when you want absolutely no sampling (blurring) of the image. Not bad to have.

Linear: Use when you have very small text; cubic interpolation is usually better otherwise. This produces blurred, but jagged, edges.

Cubic: Use for most images. Unless the image is very small or incredibly detailed, cubic and bicubic interpolation helps keep edges smooth. According to Wikipedia, it can sometimes increase perceived contrast or cause artifacts.

Lanczos: This interpolation method is much like cubic except that instead of blurring, it creates a "ringing" pattern. The benefit is that it can handle detailed graphics without blurring like the cubic filters."

So, as you can see, any serious enlargement requires the most sophisticated algorithm to prevent blurring.

This way it's easier to manipulate the result.