A little while back, I introduced the feature to mhchem to properly format $K$ constant variables, like $\ce{Ka}$ rendering as $K_\mathrm{a}$, $\ce{pKb}$ rendering as $\mathrm{p}K_\mathrm{b}$, etc. (besides $\ce{K_a}$ and $\ce{pK_b}$).
I was inspired by seeing quite some usage of Ka, pKb inside \ce, here at Chemisty.SE. I also checked if there were other meanings of these terms and found none.
But now, I am getting doubts how future-proof this is. What if the next new chemical element's name will have the 'Ka' abbreviation? What if some field will invent the 'Ka' 'nickname'?
Do you know any other meaning of Ka, Kb, Kw, Kf, Kc, Kp, Ka1, Ka2, Ka3, Kb1, Kb2, Kb3, Keq, Ksp other than $K$ constants? How likely is it that alternative meanings for these will emerge?
Or, to phrase it differently: How likely is it (or will it be) that somebody typing \ce{Ka}, \ce{Keq}, ... does intend other output than $K_\mathrm{a}$, $K_\mathrm{eq}$, ...?
$\ce{Ka}$render $K_\mathrm{a}$.\ce{}is meant to typeset chemical expressions such as compounds or reactions. $K_\mathrm{a}$ is not a chemical expression, it is a physical/mathematical one. It makes practically zero sense to include these in the same command. Remember that a core principle of $\mathrm{\LaTeX}$ is to use semantic markup — having a chemical markup for a physical constant violates that rule. $\endgroup$$\ce{Ka}$on site were people thinking ‘Ah, when my last post usingCO2was corrected, they wrote$\ce{CO2}$. So now that I haveKait should probably be$\ce{Ka}$. And in the next line$\ce{m=5g}$.’ Do you really want to account for every semantic misuse? $\endgroup$+in a chemical equation is not chemical, but a mathematical character describing a chemical phenomenon. Or one could say that oxidation states should not be part of\cebecause they are a "dimensionless number of chemistry" just as $K_\mathrm{a}$ is. I am very open for arguments to remove $K_\mathrm{a}$ support from\ce, but please don't tell me $K_\mathrm{a}$ is not chemical. $\endgroup$