Jackson LJ is right of course, it would be helpful for the Court of Appeal to give some guidance on the test laid down by CPR 44.3, but some might say the Court has missed opportunities to do so already.
The other practical problem of course is that on individual cases, there is probably insufficient money at stake to proceed to an appeal.
As someone who conducts a lot of detailed assessments, I find that proportionality in practice appears not to have too much of a startling effect. Costs Judges appear receptive to arguments that where a line by line assessment has been carried out already, there is a double jeopardy risk to receiving parties by the "stand back and look again" approach. That approach is of course arbitrarily subjective and very difficult to advise clients upon; meaning that we are left with an unsatisfactory state of affairs.
I'm afraid that the uncertainty will be with us for some time to come.
Jackson laments lack of proportionality guidance