Qt 4 will be removed in the next major Debian GNU/Linux release (Buster)
We have been announcing it: we are going to remove Qt 4 during the Buster cycle.Qt 4 removal in Debian testing (Buster)/unstable
Or at least that's the best outcome we can expect. Removing a very highly used library is hard, as Qt4's Webkit has proved. Qt 4 is long dead upstream and we have already started to need to patch it with untested patches as in the OpenSSL 1.1 case (will be in experimental in a few hours after this post).
We will try to put as less effort as possible in keeping it alive meaning that from now on if we need to patch it to make it support a newer lib or alike we will simply remove it's support if possible. Using the OpenSSL case as an example, if we need to support any version > 1.1 we will simply remove the SSL support. That means things will break.
So, if you depend on FLOSS which is still based on Qt 4 be sure to try to port it. If you depend on a proprietary vendor software which uses Qt 4 then you better start telling them it's really time to update it. Really.
We will soon start filing bugs against packages using Qt 4 (prior to proper announce in debian devel).
For the Qt/KDE team, Lisandro.