I think much of what you want to do can be handled with existing tools (so long as you don’t run afoul of some of the bugs/issues). See below for my input on those.
The biggest problem you’re going to hit is with Google Calendar-synced events and features. Gcal sync is neat but in all my years of using Legend it’s never been robust enough for me to trust it. Too many things don’t survive the sync (like prefixes), Gcal features don’t get pulled in to Legend (like attendees), and something always seems to break (currently, changes to time/date in Legend don’t push up to Gcal). I no longer Gsync events but I don’t coordinate with others so that works fine for me.
- Ability to use the “/” menu to add a calendar event into my Outline
A ‘calendar event’ is just an item with a !date assigned. So you can drop that new item into your outline in the Board you’re already viewing, or use the “new item” dialog box (hotkey is available) to create a new item and apply the !tag in there.
- Ability to “merge” or “link” a Outline section to an existing Calendar event.
Do this with a [[link or ((mirror to connect existing Legend items to other items that have !dates (i.e. calendar events). I’m not sure how well this will hold up if you Gsync though.
- Synchronized Calendar and Outlook pane locations
Try using “Highlight in all Panes” from the RMB (right mouse button) menu. Also available via hotkey.
This is not “idiot proof” – you have to make sure that at least one of the other Panes on your Board is pointed to the Document which contains your events and doesn’t have filters that would hide the item. So if your calendar holds items that come from multiple Documents, you’ll need one Outline Pane for each of them. The Board therefore needs to be structured with this type of use in mind to start with. If you have a pretty well-defined “system” and workflow already in place, this shouldn’t be an obstacle. But if you’re hunting for a misplaced or errant event, you’re better off using “Global Search.”
- Confirmation Prompt before editing calendar events (particularly ones with other meeting participants).
I don’t think Legend is able to work with “participants” at all, this one is a miss.
Aside from that, I see editing an event as no different than editing any other item and would not want the extra step of a confirmation.