I'd like to be able to use HD Link to scale my footage into any size now that I own P4K.

HD Link does have some options to scale but not to 4K or 2K or a custom size. For example scaling 1920 x 1080 upto 2048 x 1080 or 2048 upto 4096 x 2048 etc...

Is this possible?

Thanks

Yes that can happen. The main reason we did just add more reolution option is HDLink is 4:2:2, and much of Prospect 4K is RAW or 4:4:4. So there are several upgrades needed to HDLink.

Are there plans to implement a choice of YUV 422 and RGB 444 to HD Link plus chosing a custom aspect and frame size?

How soon could this be added to the list? I would like that option, not sure about other users.

It is on the list.

Awesome! In the current build or in a future one?

Look forward to it. Keep up the excellent work!

It is a while off, but in the plans.