If you need to get reviews of plans or if you need to collaborate on initial drafts of plans, you have a couple of options:
If you're using a budget bid strategy: In some serial fashion, have each person who needs to give input look at the plan in the Search Ads 360 interface. Since there's no way to lock the state of a plan, anyone with sufficient permission can modify it. If you're sharing a plan with other team members whose permissions let them make changes, keep a record of changes so you're able to revert to a known state if necessary.
If you're managing the plan manually: You have the option with manually managed plans to download a spreadsheet of the plan configuration. In this case, you can share the spreadsheet, gather input until you've arrived at a final state, and then upload the finished spreadsheet that contains the final version of the plan.