Apple Silicon in an external display? That must be really exciting! Well, not really. It is most likely something boring. Perhaps the A13’s sole purpose is to drive higher density mini-LED dimming zones a la the new iPad Pro, probably repurposing a lot of the R&D investment for the iPad into this product.
Apple’s massive economies of scale means it may very well be cheaper for them to shove in A13 chips to act as the display’s controller, compared to the cost of designing new silicon for something bespoke. The new display project is in early development stages and by the time it ships, in a couple of years, the A13 would be old. It is analogous to how the T2 chip was used in the iMac Pro and later Intel MacBooks, which was essentially a rebranded A10 SoC. The T2 served ‘boring’ duties like driving the secure boot process and SSD controller.
If you want to take a more optimistic and exciting tone, the A13 could possibly be present to enable features like Face ID. That would be neat. Timing wise, that would line up too as the rumour mill expects Apple to transition Macs to Face ID biometrics in the next few years.
More than anything though, I simply hope the next-generation display is more affordable. It would obviously still be a premium product, it is Apple after all, but there’s a big difference between ~$2000 and $5000 (plus $1000 stand and $1000 nano-texture coating). As the technical capabilities of the iPad Pro’s Liquid Retina XDR display already surpass the Pro Display XDR, a significantly lower price point seems readily achievable.