@bkamins I think you will be fine.
As an average user, it seems to me that the core functionality of DataFrames has been available for ages (append, joins, filter, select,….). I therefore think a lot of users would be perfectly fine with an older version of DataFrames.
When you ask about „whether users will complain“ that is, unfortunately, a bit of a different questions.
Now I am no expert on this, and I don’t have any statistics, but the users that are unhappy or complain, often have a high visibility (possibly warranted). But it seems that there are good reasons for the limitation to 1.6+ thus this should be fine.