The R5 HMDI 2.0 port can't be changed but using compression (Cinema lite) may allow the port to be used for external recording. Depends on the compression level. Currently, 4k60 at 340Mbps is handled. 5x compression for 8kraw would be >500Mbps so probably not but 4k/120 could meet the spec
Yep, its possible. I can't imagine the heat generated by chewing on all that data will be too good though.