FINA has been doing its thing again, and has issued a new set of rules.
The only significant thing (probably) is that in back stroke, the swimmer cannot duck entirely under water to finish – some part of he body must be above water. I have already heard informal discussions of this suggesting that race judges may be looking to penalise anyone dipping on eh finish. Of course what will happen remains to be seen, but that is not what the rule says or requires.
There are two kinds of finish which might be considered. First is the dip on the finish. This can be just a long reach for the wall with the leading hand. The hand goes under and the head goes under. The second is a much exaggerated dip which seeks to take advantage of the fact that you can be faster if completely underwater swimming with a dolphin kick. Backstrokers do not the same breathing issues as suffered by other swimmers during their standard stroke, and it may therefore be a greater temptation to make the most of not being in significant oxygen debt by dipping early and fully.
The first should be fine, the second has been outlawed.
For the new rules see: