I don't get it, why not use BYOND? SS13 is laggy because it simulates a load of stuff in not necessarily the most effective ways. For example, gasses (possibly including oxygen) are mobile objects, moving around the place, causing lag. There are probably more such examples, this being the most visible. I remember the game lagging on an older computer even when running in singleplayer mode, I could literally see it pause once every "tick". I rather doubt you could do something that'd lag it up severely with a fantasy game.
Nah, not that kind of lag. I run it very well. My problem is that if you hold down an arrow key, you go blazing across the map, and items you were dragging lag behind you, you plow into people and push them down the hallway without knowing it, etc--and often when you press a button it doesn't respond for at least a 500ms window.
I'm pretty sure that its network code has a lot of latency built in, and that it doesn't handle large batches of actions being sent from the client at once. I see the same problems on JapaneseName High, which has pretty much no background processes to speak of. And you get the same thing on games like Furcadia, though not quite as badly...that was designed more to be social than to be a 'game' game.
I'm not sure how to prevent people from running waytoofast without making the controls feel responsive, but that's exactly the kind of problem I want someone ELSE to have solved, hence why I want an engine that isn't BYOND and that may have a good resolution for that. It would be nice if holding down an arrow key made you move at a certain, constant, and sane number of squares per move, with low latency. I don't know if BYOND can do that. Aside from that, I love BYOND.
EDIT: My fantasy-ish plans at this point are something like a Shakespearean fantasy game, somewhere around the sort of Midsummer Night's Dream or Macbeth, but with somewhat ubiquitous reagent-based magic. A game lasts for seven 'days' which are around 20 minutes long, and each game focuses on a limited number of plots...a wedding, a coronation, something like that, while different groups have different goals. Probably a lot of little subplots at once, but the big plot event always happens on the seventh day. Who knows if I'd ever get around to really designing, but that's what I want the tools for.