Definitely have some concerns with sidechains. They may be a valid use case but they are not Bitcoin (though they are being sold as if they are)  and are therefore a compromise. My biggest concern though is that they are being sold as a solution to a problem we are having but as yet, they are untested vaporware. Problems are not solved with promises. And when we do have them, there is the whole infrastructure thing.

Segwit feels like it is overly complicated for what it does and I suspect it doesn't bring the benefits claimed except for a relatively small proportion of users. If you don't want to keep all the data, just use pruning.