Can we treat selectors and placeholders similar somehow, or must they be distinct?

[echeran]

For a multi-select message, we have the selection phase to choose one pattern among the group. The formatting phase is interpolating the selected pattern values to provide the resulting formatted string. Let's define the arguments used (in conjunction with selection functions) for selection purposes as selectors. And the elements within the pattern used to demarcate where interpolation occurs as placeholders.

Can we treat selectors and placeholders as the same? Or are there similarities in functionality or representation that we can make? Or are they completely distinct?

One proposal in favor of aligning the representation and functionality of selectors and placeholders somewhat closely is alluded to in this presentation (IIUC).

The case for treating them as completely different concepts is explained via the conversation here, in which arguments in favor of treating selectors and placeholders as nearly interchangeable in nature are rebutted with counter-examples from the opposite viewpoint.