I think reserving IDs is the only sensible thing to do. Years ago I ran a UO emulator and thats exactly what they did. The standard world had reserved ID ranges - if you used those for custom things they would be overwritten during an update.
Some people even went so far as to agree between themselves which ranges individuals would use - this let certain people work on specific aspects of a world and combine their efforts when wanted.
ANd this is a timely discussion. I was just wanting to make a custom item and was coming here to ask if there were any kind of designated ID ranges
