-10 < something < 10
will pass the syntax check but will fail the actual parsing (since -10 < something is always lesser than 10 and the shortcircuit will trigger). However, contrary to what we did for T214642 (where we fixed short-circuit itself), we should ban this syntax altogether. Firstly for consistency with PHP, second because this doesn't do what users think it would do: the above evaluates to ( -10 < something ) < 10, which is true|false < 10, and not to -10 < something & something < 10.
There's no need to follow a deprecation plan, as I said above this already breaks filters.