Using SC, bitcoin can adapt ANY feature instantly. Bitcoin can test this feature in sandbox (SC) and make result
a) must to have -> feature is implemented
b) nice to have -> let's wait we will see latter, SC works good
c) scam -> feature RIP
It is one of 1,000 ... advantages of SC
that's right. sidechains are essentially a laboratory of innovation akin to altcoins but supported by and supporting Bitcoin's network effect