Quick update for those who may (still) be interested. I have been running for one year on Yosemite (restored from backup after update to El Capitan that broke BCC) so I can still use BoxCryptor Classic version 1.4.
The other day I finally bit the bullet and decided to install encFS and I am happy to say that it works like on charm on my existing BoxCryptor Classic volume. Response time is as good as with BCC and I have one of my two Macs now running OS-X Sierra with no issues.
Who needs BoxCryptor and their total disregard for their customer base when you can use encFS? :)