Warning: this article contains spoilers for Better Call Saul.
Breaking Bad. Presumed dead by many, Lalo Salamanca is alive and well after Gus' failed assassination attempt, and he continues to haunt Gus from afar. Convinced that Lalo will soon strike back, Gus' paranoia shows no signs of slowing down, with Mike's men constantly surveilling Gus' house to no avail.
Meanwhile, Lalo is searching for the "proof" that he can bring to Hector and the cartel to prove that Gus is a traitor. That proof is Gus' superlab. The superlab is a huge location in Breaking Bad, with Walter White and Jesse Pinkman spending a lot of time cooking meth for Gus' drug empire there. In all that time, Lalo does not appear in Breaking Bad, leaving many viewers to speculate why. Many believe that Lalo could simply be out of the picture, retreating to some remote locale, perhaps only to reappear in Better Call Saul's Gene timeline. Better Call Saul season 6, episode 5, seems to discredit those theories, however, and hints that Lalo's fate is much darker.
Better Call Saul appears to be setting up a grand showdown between Gus and Lalo, and the superlab seems the prime location for it to happen in. Lalo obsesses about Werner Ziegler and searches his wife's house for clues, it's only a matter of time before he finds out the truth of Gus' operation and unveils his lie about his huge chicken freezer. Gus also has a revelation about Lalo's plans and hides a gun in the lab, hinting that Gus is getting prepared for their eventual conflict. The most disturbing resolution to this conflict would be if Lalo dies, and is buried in the "south wall" that he is so intrigued by, which would add a much darker spin on the events of Breaking Bad in the lab.
Back in Better Call Saul season 5, Gus Fring lies to gun that Gus plants in the superlab is another example of Chekov's Gun, and will certainly be used in one capacity or another, the south wall should also have relevance in season 6. Lalo being buried in the wall is only possible because Gus had to suspend the construction after Lalo originally got suspicious and chased after Werner Ziegler. It would be an ironic end for Lalo, who has searched for answers about the construction for two seasons, only to become yet another secret that the walls hold.
As the creator of Breaking Bad and Better Call Saul, Vince Gilligan said, the events of Better Call Saul will make viewers see Breaking Bad in a different light - and Lalo being permanently in the walls of the superlab when Jesse and Walt cook in it would certainly add an extra layer of darkness to every scene upon rewatch. Unbeknown to them, by cooking in Gus' superlab Walt and Jesse are not stepping into the big leagues, but into an arena of death. Gus Fring's true capacity for evil is only proven when he kills Viktor in the lab but the truth, and Lalo's body, would be right next to them the entire time, yet again proving that Walter White is more ignorant than he thinks.
New episodes of Better Call Saul air every Monday on AMC.