Boring update:
I've been cleaning little dents in the sculpts with magnification, as I the prototypes were sculpted without loupes, defining edges, beveling some corners, rounding others, and making the bases as thick walled as I can. Testing fitting issues, etc.
Regarding reinforcing the base of the silicone keycaps: I bought several type of fiberglass composites, which haven't had the adhesion to the silicone I was aiming to. However, I do have some solutions on the way as I've been talking to different providers from past week, that are lengthy to explain. It involves getting the fillers to stick only to the base part, to keep the sculpt wobbly, and the stem integrity. Remember silicone only sticks to itself.
The basic alternatives were to buy fillers pretreated with an special adhesive (tried that with bad results), treating them myself (I'm in the middle of getting the adhesive), or lastly, as I came across with a self priming silicone (gonna try that this week), so it'd adhere to substrates of certain type without extra effort and could be tinted in the same coloring than the body.
I wanna sort out the problem of having one solid silicone keycap and go as further as I can with it.