I've now done some testing of the game while running over a network, and as I was half-fearing, it turns out to be irritating jerky, even when just playing over a small LAN. It seems that BYOND's networking just doesn't handle smooth pixel scrolling well.
It's mostly a problem with fast moving craft (like airplanes), so it will be less noticeable for the slower-moving ships which will form the main part of the game. I may just live with the problem, though there are alternatives such as making aircraft a non-pilotable craft.
I now have a <a href="http://www.byond.com/members/Hobnob/files/warspite/warspite_dr1.zip" >demo available that shows off some of the game systems. You fly a torpedo bomber and destroy NPC ships and aircraft (which move around, but don't yet fire back).
Please bear in mind that this demo is quite different from the way I envision the final game (it's more like an action game than an RTS), there's no sound, and some of graphics are placeholders. The multiplayer support is also quite rudimentary.