I have seen discussion of CT being used on the a side chain. What are the chances it will be applied to Bitcoin Core itself?
Pretty good actually as it has become a lot easier after SegWit allowed for new script opcodes through soft forks. It might still be a few years out, as there are other priorities, but Gregory Maxwell is pretty active on CT.
This is not a question anyone can answer. If you'd asked me 2 years ago what the chances of raising the block size in the future were, I'd probably have said that they were pretty good.
I think we can all definitely agree that CT is unlikely to be merged into Bitcoin Core itself any time soon, if at all, as it would require major wallet changes across the board, and would be a massive hard fork...with all the push-back that goes along with that.