To be honest these feel like excuses to avoid structure. Keeping things consistent is something that require dedication and explicit effort. Just saying "everyone just do logging in their preferred format" seems the easiest way. Structured logging gives you lots of benefits. You monitoring will just work out of the box if you keep to the standard. Additional logs won't arbitrarily come up within your system with no anticipation. I'm not saying it will never happen, but you have control over it.