There’s a wide spectrum of options these days for making beers with varying levels of acidity. Let’s consider that spectrum: On the most challenging, complex (authentic?) end, you might find spontaneous fermentation; on the easier, pragmatic (cheating?) end, you might find direct additions of lactic or malic acid to control tartness. Then you can imagine all kinds of things out in the middle, such as kettle-souring or co-pitching bugs with yeast.
As a brewer, you choose your comfort zone; we all have different tolerances for complexity, difficulty, and unpredictability. (Then there’s the straight-up hedonistic view: If it tastes good in the end, who cares how you did it?)
So, what about these new yeast strains that produce lactic acid (i.e., they are not Lactobacillus)? Where do they fit? We previously wrote here about Lallemand Sourvisiae—a bioengineered strain of Saccharomyces that produces enough lactic acid to bring your wort down to a puckering 3.0 pH … at which point, some blending might be in order. (For context, Belgian oude gueuze tends to land between 3.2 and 3.4 pH.)