Grease Pencil -- Destructive, Real-Time Mirroring

When I say "destructive mirroring", I'm referring to mirroring without needing the Mirror modifier, which is non-destructive. While it's not perfect, and has its own limitations it allows for certain use-cases where you can work on both sides and have it be reflected on the other almost immediately.

We have this with modelling in some limited capacity, where you can move around vertices with X-Mirror enabled, and it'll be reflected on the other side. The downside to that is that it doesn't reflect adding and deleting of newer vertices (but that's a separate discussion altogether).

We also have this in Sculpting mode, where it functions quite well, and something we depend on.

But unfortunately, we don't have that for Grease Pencil, and I'm not sure why. While the Mirror modifier is helpful, it's still no replacement for tools like Krita -- Grease Pencil with Mirror Modifier can't allow real-time mirroring, nor does it allow you to draw on top of and even erase from the mirrored instance, which makes you adapt to the tool rather than the tool adapting to you.

Adding a Destructive Mirroring mode, just like in the Sculpt mode, can potentially alleviate those problems. In fact, it doesn't even need its own UI, but rather borrow what already exists in the Sculpt mode (the Symmetry options on the top-right). I sincerely believe that this could really speed up the drawing process and alleviate minor annoyances.