what height drop could a square taper hub take? i weigh about 65kg…
just a average idea?
I snapped a square taper hub on a 3ft drop once.
They already have brakes that mount on hubs 
I had one of those cro-mo square taper hubs from UDC on a 26" MUni and I wrecked 4 sets of cranks and the hub is still fine. usually not much more than 3 or 4 foot drops (funny since I don’t do that anymore and I ride ISIS)
I twisted the spindle on another cheaper square taper hub in a trials with much lighter riding.
A high quality square taper hub with high quality cranks will be just as strong or stronger than a cheep splined system, It’s just that it is easier to find good quality stuff in ISIS
Metal doesn’t generally break based on a single incident. Multiple incidents, such as hours of hopping on a cheap square-taper hub, will eventually break down the lower-quality steel and eventually lead to cracks, followed by one of the tapers breaking off.
That said, my 2002 Coker has thousands of miles on it, and the original hub. In fact, my original, 1982 big wheel (45"; hard rubber tire) still has its original, cottered hub. But during my years of constant Freestyle practice, at one point I was going through a hub every couple of months. Then I switched to the Semcycle hubs (strongest available in the mid-80s), and those lasted nearly indefinitely for my type of riding.