The format was mentioned briefly, in this thread here: Copying And Pasting Between Maps Broken I’m part of the main Stardew Valley(SDV) Community, and most of our members that make map mods for SDV, have turned to using the same method as JamieMage2005 used - using tIDE, the main tile editor for .tbin files, as just a conversion tool to convert it to the Tiled .tmx format, and using Tiled as the main editor. When we’re done, we put the map back in tIDE, and re-convert it back to .tbin, so the game can read it. Tiled is far superior to tIDE, and it would be really great if we could just ditch tIDE altogether. It’s not the greatest tool, and quite frankly most of us are surprised at how the dev of SDV even used it as well as he did.
There has been some great progress by spacechase0, about which he wrote on the issue tracking support for editing Stardew Valley maps (#1560). He seems have a somewhat generic .tbin loader as well an XNB loader implemented.
He just commented about turning it into a Tiled plugin, which I guess is not entirely a coincidence with your post here? In any case I replied to him at the issue.
Just an update on this: tBIN support is meanwhile available in the snapshot builds: