I can't comment on how well it was implemented in PC-Write but it won't be far-fetched to say that Sublime made multiple-selections mainstream. I had seen some references to vim plugins that offered that feature but it had limited abilities. The three ways of doing multiple selections—selecting multiple instances of a word, placing multiple cursors downwards in succeeding lines, and using point and click—made Sublime's implementation vastly more powerful.
Back in the day (early-mid 80's), PC-Write was kind of like the SublimeText of the era.
Multiple-select was indeed one of the key reasons to use it, as a programmers editor, even though it was intended for more general-purpose word processing tasks.
Anecdotal experience: my first unboxing of ST2 led to the proclamation: "finally, someone has done multi-select cursors again, almost as good as PC-Write back in the day!"
