I think this would be a great thing to add. But the difficulty is how the TD currently computes statistics. It goes through a few phases:
- Look for all tournament files in the specified locations
- Filter out the tournaments that don't match the stats profile
- Go through the tournaments and get a list of all players
- Filter out the players that don't match the stats profile
- Go through all remaining tournaments and compute stats for each player in each tournament
By the time it gets to the last step where formulas are computed, we have a bunch of "player statistics" objects that contain all of the computed statistics. This is used to compute the formula values. To use your example:
sum(last(10, scores))
... at this point the scores variable is a list of the scores computed from the Tournament Scores formula. But those scores are no longer associated with specific tournaments. Functions like top(...) work fine because they only care about the score values themselves - they don't care which tournament they belong to. That connection is gone. But to implement something like last(...), we have to keep an association between the value and the tournament, so we can sort those values by tournament date. It's not impossible, it's just not how the stats were designed.
tl;dr: you can't do it today, but could be a future enhancement.