So it is possible to use Timelines in formulas. For automations, the start and end dates of Timelines work (in many cases) as Triggers, however there are no automations currently that can be input or modified via actions (Such as “set today” or “push”). That makes them limited.
The issue that my post resolves is using mirrored date/timeline data in formulas.
For example: You may have a high-level (let’s call it “Projects”) board that connects to a low-level (let’s call it “Tasks”) board. By mirroring a date (let’s call it “Due Date”) column from the Tasks board onto the Projects board, where you have a one-to-many relationship, you would end up with a summary of due dates. This is presented as a Timeline in the Projects board and gives you an approximation of the Project timeline, sourced directly from the task due dates—something obviously useful.
The problem is that you cannot use the start and end dates of this column in automations or in formulas. My solution does not allow it to be used in automations (although there are other workarounds for that), however it does allow you to generate start and end dates that can be used in formulas.