Packaging means "better than just loading something and having it pee in the global readtable". It doesn't solve the problem that read macros compete for the same characters and clash.
Documentation for merge-readtables-into:
"If a macro character appears in more than one of the readtables, i.e. if a conflict is discovered during the merge, an error of type READER-MACRO-CONFLICT is signaled."
Exactly, and this is awesome. If there is a conflict, I get an error and can decide what to do.
At their core, reader-macros are abbreviations. Obviously there are a finite number of abbreviations one can use, so any time you want to add concise syntax from more than one source, there is a chance of conflict.
I can see how this would have value if your idea of Lisp programming is to bring half a dozen new read syntaxes, and use them all in the same source file. Plus keep up with upstream enhancements in all of them, so you have to guard against new clashes popping up.
