My take on this is:
His next contract will almost certainly be his last opportunity for a major pay day, given his age, so he's probably going to want a 5 year deal like Bregman got this year. Are the Cubs prepared to make a 5 year/100 to 110 million $ commitment to him?
He will almost certainly get it from someone. Seems like the Yankees have loved Happ forever and wouldn't surprise me if the Angels and Mets are also interested. Do the Cubs want to get into a bidding war with other big market teams for Ian Happ on a 4-5 year deal that could run over 100m?
So is he "worth" an extension? For another team - yes (imo) but for the very unique needs of this team, I personally wouldn't. They have to buck the status quo somehow and assuming they want to keep Suzuki around, LF is probably the only opportunity to find a true elite hitter.