Suggestion: refer to other scheduled tasks in DEADLINE/SCHEDULE

[hugo]

Sorry if this has been asked on the list before -- I searched briefly
and couldn't find anything.

I use org mode for scheduling events (which are not tasks, and therefore
do not have a TODO status) as well as for logging tasks (which do have a
TODO status). Often, I find I want to set a deadline (less often, a
schedule) for a task identical to the timestamp of an event (e.g.
there's a seminar on Thursday, in time for which I need to read two
papers).

At the moment, I do this by looking up the event, copying the timestamp,
then setting the deadline in each task to that timestamp. This is
laborious, often quite fiddly, especially if the event's timestamp
repeats (as with weekly seminar), but the task only relates to a
specific instance of that repeat (the paper I need to read has to be
read in time for /this week's/ seminar, so I have to look up the
timestamp and check what the next match on the repeater will be, then
input that manually).

I think it would be great if other org headlines could be referenced in
DEADLINEs and SCHEDULEs. This would effectively solve my problem: I
could just add an id (or whatever identifier the implementation ends up
using) to the event headline, and then use that id in the DEADLINE or
SCHEDULE, thus:

,----
| * Important Seminar
| :PROPERTIES:
| :CUSTOM_ID: seminarid
| :END:
| <2022-10-27 Through +1w>
|
| * TODO Read Famous Paper
| DEADLINE: seminarid
|
| * TODO Read Other Paper
| DEADLINE: seminarid
`----

Then the tasks to read papers will show up in my agenda with deadlines
when the seminar starts. As far as I know, there isn't a way to do this
already (though if there is, I would be happy to use it!).

This would be great, but it still doesn't solve the repeater/specific
date problem. For this, we would need some sort of special syntax which
selects one out of the various correct dates. Perhaps:

,----
| * Important Seminar
| :PROPERTIES:
| :CUSTOM_ID: seminarid
| :END:
| <2022-10-27 Through +1w>
|
| * TODO Read Famous Paper
| DEADLINE: :id seminarid :after <2022-11-08 Tue>
|
| * TODO Read Other Paper
| DEADLINE: :id seminarid :after <2022-11-08 Tue>
`----

(This is only a suggestion, to demonstrate that some special syntax
would be necessary. I'm not wedded to the use of keys, or the specific
keys I have suggested, or anything like that.)

I don't have the knowledge of org, or the time at the moment to
implement any of this (though I wouldn't be upset if somebody else
did!). At least for now though, some questions:

- What do people think of this as an idea?
- What would be a good solution to the extra syntax problem?

(a similar question seems to have been asked before:
<https://emacs.stackexchange.com/questions/62590/org-mode-how-to-set-a-deadline-to-an-already-appointed-meeting-date>)

One day, I might find some time to look at the codebase and implement
this if nobody else does..

thanks,

Hugo