For now one can only donate with Bitcoin. It would be cool if they could also donate with Bitcoin Cash as fees for this cryptocurrency are much lower as you can see here:
https://bitinfocharts.com/comparison/transactionfees-btc-bch.html#3m
I know that $3 for a fee might not seem like much but for $15 donation its 20%. And its $3 that could have gone to GnuPG.

If you decide to add Bitcoin Cash address on the donation page, I recomment posting address in the new BECH32 format. More about it here:
https://www.bitcoinabc.org/cashaddr