Rebol2 had a very well-known irritation, known as "lit-word! decay":
rebol2>> word: first ['x]
== 'x
rebol2>> word
== x
rebol2>> :word
== 'x
It was much maligned, and R3-Alpha and Red stopped doing it.
But as bad as it was... even the term itself: "decay" (chosen by those reporting the "bug" after the fact, and it may be that I was the one who called it that)... foretold the need for isotopes.
I will point out at least one important difference from modern Ren-C isotopic theory: if I were to embrace this particular bad idea, it would look like this:
hypothetical-rebol2>> word: first ['x]
== 'x
hypothetical-rebol2>> word
** PANIC: WORD is a LIT-WORD! and maybe you didn't mean that.
hypothetical-rebol2>> :word
== 'x
hypothetical-rebol2>> decay :word
== x
And that's how modern unstable isotopes work! But we don't do that for ordinary values you might pick from a BLOCK!, or whatever.
Hence of course I'm not agreeing with the premise of decaying quoted WORD!... I just think it's interesting that even the terminology ("decay") did come to bear on the actual solution. The real answer has actual meta-representational value and puts you in control, as my hypothetical-rebol2 does.
So it would be misguided to say this foretold "isotopes" in the Ren-C sense of what they actually became (if you want evidence that what I have built is not "obvious" from Rebol2 precedent, just ask any Red person who says isotopes are making the system "10x more complicated than the problems they solve" -- a direct quote from the willfully ignorant... but they shall see the light, one day. 
)
But, the correlation of the word "decay"...and the spirit of the desire to "gloss distinctions when the situation warrants" is undeniable. Certainly I was influenced by the phenomenon and terminology, even if it didn't really line up with modern methodology.
I was so anti-lit-word-decay that I must have blocked it out of my mind, to not even realize "decay" was fundamental to Ren-C isotopic theory. (Although if it were me who coined the term, that's maybe less surprising.)
But if you squint real hard, you might see it being related, sort of. Hard to say because before the LIFT_BYTE the entire vocabulary was restricted. It's like not having parts-of-speech, no adjectives, no verbs, talking only in nouns... so nothing could be carried by values themselves, all meaning had to come from the function calls.