Using UART4 to stream data to a Rpi4

Hello,

I saw in a previous post that the current firmware only supports MFAM streaming via Ethernet, and that UART5 isn't supported. I'm modifying the Dev Kit firmware to add TX output on UART4 instead, by adding a parallel Mailbox_post in spiTaskFxns.c to a new UART4 TX task/mailbox, at 460800 bps.

Before going further, I wanted to ask:

1. Is there any hardware-level reason UART4 wouldn't work here, beyond it just not being implemented in the stock firmware?
2. Does the existing SPI→Ethernet pipeline assume a single consumer, in a way that could cause timing issues if I add a second parallel mailbox post for UART4?
3. Has anyone tried UART-based streaming from the Dev Kit before, and if so, any known pitfalls?

Thanks in advance!