Multiple outputs has been suggested before, which is still something I want to add. Thanks for showing interest in that, it tells me people really want it! 😁
In FL, the slide notes are exclusive/specific to FL-based plugins, so they can not be handled by external VST plugins unfortunately. You can, however, use midi pitch automation to make pitch slides.
I'm not entirely sure what you mean with the "boing-pitch" effect after listening to Frequencerz - Burning, unless you mean the very long pitch-automated tails? I guess you could technically do that with either a longer sample, or by enabling the loop function in Nimble Kick.