Can you say "ça est une idée brillant?
Freeform Writing Exercise A1
For elision, my understanding is that we don't have vowels together as you suggest.
So we don't use ce est but c'est therefore ça est would be unacceptable in terms of elision.
Hope this is helpful.
Joe, just for completeness to add to Jim's answer, as you have written '... une idée brillant' in your post.
It would be ' c'est une idée brillante ' with adjectival agreement with idée - it is only stand-alone adjectives following c'est that are invariable (masculine).
Since I'm not really sure if you're asking about subject doubling, which is a common practice particularly in spoken French, let me address this issue as well:
C'est une idée brillante ! -- This is the standard form and considered "most" correct.
Using subject doubling for emphasis, you often her these versions as well. But I wouldn't use them in formal or written French:
C'est une idée brillante, ça !Ça c'est une idée brillante !
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