So far, I used the most portable format I can think of: the command-line-based format:
importdescriptors "[{\"desc\":\"tr(cMahea7zqjxrtgAbB7LSGbcQUr1uX1ojuat9jZodMN87JcbXMTcA)#tnrke5yz\",\"timestamp\":\"now\",\"label\":\"taproot\"}]"
importdescriptors "[{\"desc\":\"tr(cMahea7zqjxrtgAbB7LSGbcQUr1uX1ojuat9jZodMN87K7XCyj5v)#xpd75frm\",\"timestamp\":\"now\",\"label\":\"taproot2\"}]"
It is standardized across wallets, it is extensible, and it is reasonably-compatible between different versions of Bitcoin Core. Also, in case of incompatibility, it is quite easy to fix it, and convert into another version of Bitcoin Core.
Descriptors are great but they're not human-readable, which is probably why the BIP doesn't make use of them.
Of course, it is a good idea to make the first column of the CSV records a descriptor instead of an assorted collection of addresses/transactions which require another column to differentiate. In fact, if descriptors are used, we can completely do away with the 3rd "type" column.