This is a proposal to hopefully avoid xruns. I don't experience them often, but once in a while is already too much.
The idea is to downgrade the rendering sampling frequency before hopefully overloading occurs. For instance, if the CPU load goes above 80%, then for the subsequent audio buffer, it would divide the sampling frequency by half, going from 48KHz to 24KHz, and put it back up to 48KHz as soon as the load goes back under 40%. The jack frequency wouldn't change but the host would make the engines/plugins believe that the host frequency has switched to 24KHz, then the host would stretch and interpolate with an inexpensive LPF or such. Of course for that to work it assumes the engine/plugin can switch it's rendering frequencies without producing glitches, this is the hardest part I think, but since all these are free softwares, this is probably addressable by the community.
Of course one would still want to avoid rendering at lower frequencies, but this would be used as last resort when all parameter configurations to avoid xruns have failed.