Ehh. While new exchanges are always good for better competition, new exchanges != adoption; in my opinion at least. In the case of Line's built-in crypto exchange, it's probably just another 'feature' of the app that most non-crypto people are going to ignore. Though I'm definitely not complaining, if anything, this just gives more legitimacy to bitcoin or cryptocurrencies to those "bitcoin is a scam" people, but it definitely doesn't guarantee adoption.
I see it the other way though. Once a person or a company uses a technology, it is adoption for me. Whether they wanted to take advantage of the technology or the potential profit it may bring, once a technology is embraced and implemented it is an adoption.
And we both agree in a certain degree that these institutional company that "adopted" (possibly added in your term, referring to the bolded one) Bitcoin will help prove that Bitcoin is not a scam. Anything that can clear the doubts of the masses towards Bitcoin is a good move IMHO.
Some persons are waiting for their government signal to tell them that bitcoin is the way to go in this and next generation, I am scared they might have loss too much before their government finally speak out, they just might have loss out much from what we are enjoying. More tech giants will follow the step of Gram.
Indeed with these institution embracing Bitcoin and approval of financial institution for sure those who have doubt in Bitcoins may acknowledge that Bitcoin is not a scam.