PBS currently use a single http2 connection per backup. A future plan is to use http3, but I do not
think that can saturate a LACP connection. So, no - there are no plans to optimize for LACP.
The chance of a collision is lower than winning 8 lottery games in a row, see
https://pbs.proxmox.com/docs/technical-overview.html#notes-on-hash-collisions