Don't worry, LG hasn't given up on modules for the LG G6!
However, LG spokesperson Ken Hong wants to disperse any such rumors before they become prominent. According to him, the V20 was conceptualized and design choices were well in their final stages when the G5 was released, and the sales figures of the latter made little impact on the V20's final form. Apparently, the company just didn't imagine the phablet as a modular phone the way the G5 is.
Additionally, Mr. Hong continued to say that LG is still dedicated to making modules work, and next year's G6 will develop the concept further. Whether this would bring more variety in modules and whether they would be interchangeable with the G5's add-ons remains to be seen, of course.
So, there you go. Despite how the LG V20 made it look for a while there, LG modules are not dead!