The link to the original 2010 post: https://mathoverflow.net/questions/28334/how-should-the-math-subject-classification-msc-be-revised-or-improved
Since it has been 10 years since this question was posed on the Math Overflow forums, and the Mathematics Subject Classification has gone through yet another revision (2020 edition), I thought I would repost this question to garner some new and updated feedback on the matter.
The 2020 Mathematics Subject Classification (MSC2020) has tried to revise and improve on some of the problems that MSC2010 faced, one of the major ones being the addition of computational aspects to many branches of research as well as large additions in content such as to the field of dynamical systems. However, what are some fields of research that have yet to be revised or improved on (or even added) that you feel should be taken care of in the next revision?
My answer: As many have said before me, there is still the lack of a broad classification code for both Quantum Algebra (which is a category in arXiv) and Lie theory. While many people have suggested the addition of these two branches as headings, it seems that ZBMath is still not ready to assign a classification code for both of these.
Note: Many people have commented on the disadvantages of classifying branches of mathematics into distinct groups when they are so inter-related (which is how the MSC is structured), however this post is targeting the issues in MSC2020 regarding how it is designed to be used rather than how it isn't, although feedback on how the MSC should be reorganized or redesigned are also welcome.