AdiIRC

Both clients can do that. I do not understand why you're arguing like that
You're basically arguing that addding floor division to $calc did not have the (same) potential of breaking scripts, whatsoever.
But that is not how it works (unfortunately): before adding floor division to $calc, (let's make an example)my script was expecting 0 from using floor division, now, my script is broken because I don't get 0. That's how it works.
So with regard to that, I hope I demonstrated there are equal chances a script may break from adding floor division to $calc than adding it to /set, therefore since it was added to $calc, it makes no sense not to add it to /set.

It could be a waste of time for adiirc, this report was initially made when talking about mIRC, which has terrible $calc performance, with time sensitive script such as online gaming, using set -l %var N // N2 is far faster than the equivalent set -l %var $calc(N // N2), still a bloat from many perspectives, but asking for fast $calc is not an option in mIRC ;)

Having $numtok and $gettok(,0,C) is definitely a bloat, this one is a very soft bloat compared to that.

If mirc decides to implement this and break backwards comparability, adiirc will follow, until then, adiirc should be compatible with mirc as it is today.

Yeah fair enough, I did suggest it for mIRC but it didn't get added so maybe you guys have the same feeling on backward compat.

I don't really care that much about backwards comparability, I only care about mirc compatibility so scripts written for mirc in most cases also works the same on adiirc.

If not for mirc compatibility, there would be no point in having msl in the first place, there are better languages.