We are confident, as per Apple's June 2018 announcement of the MacOS Mojave version as their next OS, that FocusTune will run under Mojave. However, we are also confident that this is the last MacOS in which this will be true. So as of now (June 2018), it looks like we are "safe" for another 1.5 years (winter of 2019).
As for beyond that....
It is simply cost prohibitive to re-write our application for 64-bit mode. The tools that we use, are not adaptable to simply re-compile the app into 64-bits, so a complete re-write using a different development platform would be required. There would be no way to recoup that investment, remembering that our user base is about 50% Mac and 50% Windows (and Windows users are not affected).
Please feel free to ask any additional questions or concerns..