Would love an undo button for placing things on accident.
How could this be done?
Maybe force pause the game while building, and this enters build mode. In build mode things can be placed and removed with full refunds until planning is complete and when un-paused the changes are made final which exits build mode and finally purchases the items.
There also needs to exist a way to move things that you have already bought, but maybe has a small movers fee to move it to a new location within the factory - paying for employees labor. For example using the blueprints feature to designate a difference between placed objects and object that will be moved and the objects new location that you want it moved to. This might require a new visual layer within the game for another movers view, but would make the game a lot more playable and plan-able for end game, longer play-throughs and for more serious players. Being able to toggle between existing placements and the new placements would be quite handy for complex and/or massive builds to ensure the move is thought out and planned correctly. This would affect game-play balance because you don’t have to sell your old equipment anymore, you just move it to a more fitting location so that you can plan your newest production line with the latest equipment and features available. However I think this is a good thing because it allows the player and the AI to be a lot more competitive because the initial cost of buying equipment is now a long term investment rather than a short term one, and maps that are bigger will be much easier compared to smaller maps due to not having to buy and plan an entirely new production line to replace the old one in the middle of the game.
Lastly solve the issue of removing stations or conveyors and having cars that you invested money into disappear. Players should somehow be compensated for this loss of investment. One way that Cities Skylines handles cars that are on a road the player deletes in build mode is they have the AI update and drive the car to the nearest road at its current location and continue the path-finding. Not sure what the best solution is, just an idea. Obviously if you go with that for this game you might need to introduce a recycling station or disassembling station for a car that has been discontinued for parts that can then be put back into storage and the frame reused for an active car model with features that are more fitting for the current market so that the AI can find a destination to send the car to now that you have removed its original stop. Then the car can path-find to these stations and solve the issue of players disappearing money and make it interesting at the same time. I could also see this being useful for cars with defects being scrapped for parts and remade with the defects being recycled materials and create an achievement for having 0 defects sold in a factory for X number of hours / days/ weeks/ months etc. this could then affect marketing via the reputation of quality your production line brand holds and could sway the buyers concept of brand value or loyalty to some extent to increase profits, think of it as a long term investment.