It's not a difficult problem to solve at all.
I used to be a pub manager in a previous carreer (early 1990's) and we were using flow-controlled pumps for beers back then. No complex electronics - just a simple activation switch for the pump, which was invariably of the rotating-chamber type. there's usually a pressure-assist in there to help with maintiaining an even volume of fluid regardless of how gloopy it is.
... and let's also face it. Different beers don't have /that/ much variance in their gloopiness.