Button/Rule formula cannot set only half of an uninitialized Date Range

[Chr1sG]

To be fair, I would like it to be possible. The alternative is two separate date fields, which is less intuitive/user-friendly.
In my case, it relates to this issue as well:

Show entities with no end date on timeline

Sometimes, I have entities which have start and end date fields, but for which the end date is not yet chosen (like projects that have started, but who knows when they will finish). They don’t currently show in the timeline view as it is now. Would it be possible to add an option to enable/disable display of such items (so that an empty end date field corresponds to a date infinitely far in the future)? Of course, I could also imagine it would be useful to do something similar for items with n…