As expl3 gets more use, it's important that the team maintain
'stability' while still having the possibility to alter the code. To
help this, we're move toward a situation where deprecated commands are
removed only very rarely. The updated approach is that removals will
(ideally) happen only once a year, over the Christmas/new year holiday,
and that we'll therefore give at least one year notice for any removals.
There are still places we need to fix 'in place' problems, which will
have to be addressed separately: there are very few of these anticipated.
This updated approach applies to code in l3kernel/l3packages and marked
as 'stable', not to for example the more experimental code in
l3experimental or 'possible additions' to l3kernel. However, it does
cover most of the core code. I do hope this makes sense.