Does it make sense to vacuume brined meat? Why not sous vide in water directly?
Theoretically, there is no problem with your logic. In fact, during the early days of restaurant sous vide adoption, when chefs were using the same immersion circulators that scientists were using, it was not uncommon to poach fish directly in oil using an immersion circulator.  Those original tools could handle that job. However, most home sous vide devices of today are designed only to circulate water.  The biggest issue I see is the mess (at best) or the destruction of your circulator. Also, it is possible to over-brine a product.  So, you may not want to cook in a brine for that reason as well.