Is it possible to add a Pre- and Postroll function to the removing silence dialog?
I use this function a lot and I am not often very satisfied with the very short preroll and the automated fade in (which is good, but cuts the first amplitude)
Everything is possible. Is it likely? It is way down on the priority list from anyone currently writing code.
Its very likely in other DAWs, thats why I miss it. 
Maybe another wish: maybe add the feature “only cut through zero-line-crossings” (when the waveform hits the middle line). Avoids clipping as goog as a small fade.
“zero crossings” are a bullshit concept leftover from DAWs that don’t expect their users to really understand digital audio.
Most audio signals contain relatively few zero crossings (compared to the number of samples). Moreover, almost ALL zero crossings are not actual sample values. This means that if you want to limit an operation to “zero crossings” you have to (a) use one of only a relatively few sample positions in many common audio signals (b) convert a non-zero sample value to zero, thus introducing distortion into the signal.
As LeatusPenguin noted, we automatically apply a short fade in/out (64 samples by default) which removes the need for “zero crossing” nonsense. However, even such fades are not capable of addressing truly pathological situations (e.g. an enormous (out of range) sample value just somewhere inside the fade). Such situations, thankfully, are rare in almost all real world workflows.
I know there is a small fade, thats why I mentioned it. For some its not the only solution. But okay, so far it works.