I assume by terrain merge, you mean placing a new terrain and making it seamlessly transition from another terrain. Right now, this is possible to do by hand, but really tedious. Still, it's hard to imagine how a "merge tool" would work. Would it extend the slopes and terrain at the edges by a certain amount? Just don't know how useful it would actually be unless they just did a stellar job with it. But I think I'd rather Larian spend their time doing other things.
