FTP over TLS support will be mandatory. In 3.10.0, opportunistic FTP over TLS to strengthen security was introduced with overwhelming success, thousands of broken servers have been fixed in the process. To further tighten security, FTP over TLS will soon become mandatory, the fallback to plaintext FTP will be removed.

32bit FileZilla for Windows will be dropped. Data has shown that more than 99% of all users have a 64bit capable CPU. If you're still using a 32bit Windows and want to continue using FileZilla, simply upgrade to a more modern operating system.

UTF-8 will be required, fallbacks to other encodings will be removed. As required by RFC 2640, use of any encoding other than UTF-8 requires explicit negotiation. Unfortunately the negotiation procedure isn't specified and hence other encodings simply cannot be used.

Support for the LIST command will be removed. In its place MLSD will be used as defined in RFC 3659. The problem with LIST is that its output isn't specified. As such it is impossible to reliably obtain directory listings using LIST. MLSD on the other hand uses a well-defined listing format. MLSD has been introduced more than 8 years ago, by now all server administrators had have more than enough time to upgrade their servers to be MLSD capable.

Once the new version will be out, old versions will stop working. There's already code in recent versions that prevents them from starting past a certain date