I've worked these past months on getting spectator mode for seats to work. What this means is that you can now lock the first-person camera view while inside the seat, and even have the camera go upside-down!

Changes

• [Improved] Seat Attachment greatly improved
  • New spectator first-person locked view mode
  • New icons and menu layout
  • Shows ingame where the seat is at with a dummy player model
  • Better support for SmoothCoasters
  • Bugfixes and many more combinations of modes supported
• [Fixed] Passengers getting stuck when warping out of a train with nobody nearby
• [Fixed] Switcher sign was not executing path finding rules by default anymore (if no statements match)
• [Added] Reroute status command, made millis-per-tick configurable, performance / OOM fixes
• [Added] The /train collision mobs command was absent
• [Added] New /train menu add and subtract commands for configuring editor values
• [Fixed] Station sign acceleration value syntax did not work
• [Fixed] Changing a spawn sign with commands did not refresh its behavior
• [Improved] Train ticket assigning commands have auto-completions now
• [Added] Attachment anchor 'cart' (position at root)
• [Improved] Performance improvements in the rail lookup cache and rail path maths
• [Added] Keepchunksloaded command train selector
• [Fixed] The destroyall command did not always remove unloaded trains since MC 1.17, and can now be set to ignore vanilla carts
• [Added] Made the behavior of push/destroy/damage collision modes being ignored when from behind, configurable