There’s nothing preventing that - it’s not expensive in computational/DSP terms at all, just a moving average of the rectified input signal. In fact if you low-pass filter the external input on one channel and tehn set a neighbor track input on the next channel with AM of another oscillator, you can achieve something similar - not the same, but similar. If you’re processing external drums then it’s ‘good enough’ to get some interesting effects. But I hope they will put this in, it would open up a lot of possibilities. Cross-modulation is the weak point in Elektron synthesis, I often wonder why they can’t handle self-modulating LFOs.