I would like to have a formula that simply inserts the row number into the cell (the number corresponding to the document or note folder).

I am assuming that many of the functions don’t really work with GS Base since there is no way to reference cells (other than within the current row by column name) or arrays?
It seems to me that many of the functions aren’t that useful if limited to constants (must of the examples use constants)?
Am I not thinking correctly?

The functions that can be used usefully within a row or to summarize a column or with constants are useful but not otherwise?
Again, am I not thinking correctly?

Perhaps not that many. This will probably be a few functions in the “lookup” category and a few summarizing functions. You’re right, they will have limited usability when used with static arrays only.
However, extending them to use e.g. entire columns would probably have limited usability as well due to recurrence issues etc.

It’s possible that their “cross-table” counterparts will be implemented in the upcoming updates.

I believe some record numbering function(s) will be added soon. (Actually, it was present in some older versions.)