Hey welcome and thanks for chiming in.
I have to agree that most home users have no idea what MTU they are using, and it is typically going to be 1500 for their LAN. Their internet will be 1492. The internet is bandwidth limited anyway, it is best left alone.
The LAN MTU however, most power users (even amateur ones) will make use of jumbo frames. Especially people who use backbones with greater than gigabit speeds (like myself).
I believe Synology even ships their NAS systems with a default MTU of 9000.
If you want to test if jumbo frames are working between 2 nodes in your network, it is actually very easy to do.
Assuming you have a 9000 packet size set:
ping <target ip> -f -l 8973
will return a "Packet needs to be fragmented but DF set." message
while
ping <target ip> -f -l 8972
will return a normal ping reply saying "bytes=8972 time<1ms TTL=64"
When you get a ping reply with such a forced packet size, you also immediately know that your backbone/switch supports the forwarding of jumbo frames.
The use of jumbo frames with Moonlight might just be enough to stress the cpu a little less and thus you might be able to up the streaming bandwidth somewhat. An estimation? Max 10% gain, something like that. But on a raspberry pi, for a single core decoding application, you take any gains you can get ;)