First - great job on this. I really like the tool. After using it, I came up with a couple ideas that might be handy to implement. Unfortunately I don't have the time nor expertise to work on creating a PR for this. The following are things I feel would take this to the next level.. they are listed IMO priority order.

1. Make the timeline sortable by timestamp (if this is already a feature I failed to find out how)
2. Add the ability to have response actions captured in the visual timelines. Right now, a MITRE tactic is required for thing sot show in the timeline
3. Have a dropdown for Event System and Remote System, referencing the systems in the relevant sheet
4. Same as above, but users
5. Add the ability to add plain text or one of the dropdowns (for most dropdown selectable items)
6. Add ability to duplicate an entry (in any sheet)

I understand the more dropdowns you add, the more formatting the SOD would require. I think these would be valuable features though.

Let me know what you think.