I think theoretically it could be possible. Your idea of 90% of C and 10% of Si, it could be viewed like a variant of our kind of life. It's interesting this idea because you don't talk about a different kind but a variant. But we can think also if in a planet you can have long chain of C like here, what's the motive that pushes life to have that little amount of Si in the long chains? Fortuity? Environment? If you think about our life history, today we know only one kind of life, but we don't know if there was other. Maybe yes and maybe it didn't work as well as our kind of life in our biosphere. So we don't have absolute certainty but we can talk only about of what we know. Before the oxygen increased considerably in our Earth, we probably had a reducing atmosphere, we have lots of Si in Earth, but the evolution life we know use the C, that is in low quantity than Si in our geosphere. Probably because it has the unique features to sustain life in this efficent way. But again, your idea is not to have life only with Si, but with a little amount and so C remains the main. So you don't upset our kind of life but you think about it only with little changes. Therefore I don't exclude your idea. For what we know probably water is essential for life because it has unique features like C that permit to support it (at least ours). But we can’t exclude e.g. ammonia as solvent. There are some organisms that use arsenic instead of phosporous. And there are lots of others exceptions in our life because it adapts. But the modifications are seen in secondary process and not in the fundamental structures. The motive is problably that it’s so hazardous to change something the is stable. Infact the modification of life is random change with constraints. But this is not mean the modification in the fundamental structures are impossible. Life process tries always to optimize its cycle according to the features of the environment (climate, chemical element cycles, atmosphere, star light, core planet, etc.) and if there is, also other life. And life modify the environment, determining also extinctions and explosion of other biodiversity. In base of “reasoning” that life does, your idea is theoretically possible if the environment offers like the most efficent solution your idea and there are the right condition for habitability/origin of life. And maybe after, the same life modifies its fundamental structure to optimize for the new environment that it built. Write me what you think. I hope to give you information to keep thinking about your idea and to evolve it. Your thought is interesting.