Curiousity got the better of me, and I just tested it in Infinite Mac.

The HyperTalk editor is indeed limited to 32 kB.

It's certainly possible that this limit only applies to editing scripts, as it's unlikely TextEdit was used in the process of interpreting them, but I don't have time tonight to investigate.

Later versions of HyperCard supported OSA scripts as well, now I'm also curious what the size limit is for (presumably) compiled AppleScripts stored in HyperCard stacks.