What is the absolute maximum salt-to-water ratio of a brine for Lacto-Fermentation There are various lacto-fermentated sauce or pickle recipes making use of a salty brine. And depending on the food item that's going to be fermented and also depending on the sense of taste of the recipe developer, the salt-to-water ratio (salinity) in such recipes varies quite a lot.
What I'm wondering is, what is the maximum amount of salt you can have in a brine; so that you can still have the lactic acid bacteria develop. Where's the cut-off point (in terms of salinity) that stops the fermentation?
Fermented Fruits and Vegetables: A Global Perspective appears to be a good document. This chapter contains some information that will be helpful for you.  In section 5.6.3, it states:

At the highest concentrations of salt (about 60o salometer) the lactic fermentation ceases to function and if any acid is detected during brine storage it is acetic acid, presumably produced by acid-forming yeasts which are still active at this concentration of salt (Vaughn, 1985).

So, 60 degree salinity halts lactic fermentation. That's about 16% salt.