Official comment
Hey recoil2,
Please understand that when you purchased the license for rekordbox 5, it was not a license to use any future versions that came along as well. Much like any other commercial software, a major version update requires the purchase of that version separate from the original. In our case, we moved from a single-purchase license model to a hardware unlock and subscription model when the new version was released. You are able to continue using rekordbox 5, which you purchased, as long as you have a computer that is capable of running that software.
If you were to move to rekordbox 6, you could use either the Core or Creative plan to use your controller. The Creative plan doesn't require that you use Dropbox, nor does it even necessitate purchasing a Dropbox subscription if you aren't putting more music than you have in the 2GB+ free plan.
I'm sorry you feel this is a cash grab - it's not; we're moving to this new model to allow for users to subscribe and receive updates and new features added to the software without having to pay for add-ons or major version upgrades.
Thank you for your feedback.