"Indeed, researchers have proposed several quality models with various sets of characteristics over the last 30 years. I doubt we’ve heard the last word on quality models."
In this quote, quality models would be referring to a high grade or well designed product or system.
"I doubt we've heard the last word" is an expression, but it can also be understood very literally. The speaker does not think that the subject he is discussing has nothing left to say; he expects to hear more from it. Therefore, he doubts the information relayed to him was the last word from the subject.
In this case, the subject is the "quality models," and the previous sentence tells us the speaker is referring to what the researchers have been proposing for various models over the last 30 years.
So, altogether "I doubt we've heard the last word on quality models" could be understood as "We can expect more updates on quality models in the future."