This would be handy for so many reasons:

1: As a back up so that if I mess the data up on the site, I can reimport my data back in easily again.

2: If I have a test CSV, I can experiment loading that in, and then load the real CSV back in again.

3: As a way of helping me understand the tagging system, so I can apply the tags to the new year's CSV. A lot of last year's return was edited and reconciled online, so there'll be tags put automatically into the CSV from your system which may be useful to see.

4: On the off chance Koinly ever goes offline, I'll still have my data.

5: And finally, closing the loop: Exporting and reimporting the entire tax data allows for consistency checks by making sure the data is the same as before, and so may help your team to spot minor bugs that might have slipped by.

If you do add this feature (and I really hope you do), please add a column to specify the 'wallet'. This will mean I don't have to save many CSVs (each representing independent wallets). Instead, they can all be inside a single TRULY universal file. Likewise, when importing data back in, I would only need to load in a single giant CSV representing multiple wallets, and online they would each be fed into their respective wallets.