This is an interesting development considering Rolf Furuli argued the brackets were unnecessary when discussing Col 1:15-20:
Thus, there can be no doubt that from a linguistic point of view, the translation "all other" is perfectly legitimate in Colossians 1:16-17, 20. It is not mandatory, but it is possible. This means that the brackets that the NWT uses around "other" may be removed, because the word "other" is no addition or interpolation, but in a given context is a legitimate part of pas. The Role of Theology and Bias in Bible Translation p. 254.
Watchtower literature has on occasion taken up suggestions first presented in independent Witness apologetic literature, as when the reference Bible reproduced Nelson Herle's tables comparing translations of anarthrous predicates in an appendix. However rumour on the forum has it that Furuli is not exactly popular with CO's and higher-ups, being at odds with the current view of higher education, so maybe it is just a coincidence the Society appear to be following his suggestion on this issue.
Plus it is not clear to me if Furuli is arguing only in relation to this passage that the brackets are unnecessary or seeking to make a more general case for removing brackets as the recent NWT editions seem to have done.