The OED does give some obsolete senses of economic as a noun, but in contemporary usage - i.e. the last 300 years or so - it is only used as an adjective. From now on economics will be allowed.
Yes, indeed, there are quite a few other words in the same boat: please feel free to make suggestions about other such words. I notice that there are also some -ics words that are not excluded as plurals. A few of those (physics, sonics) were accepted following specific requests, but all the others are ten letters or longer. Acrobatics, aerobatics, astrophysics, gerontotherapeutics, etc. It seems that I tried to identify those sort of words when I was extending the word list for ten-letter puzzles, and then for words of any length that might come up in 7-by-many puzzles.