Earlier quoted context omitted.
It already is: arxiv.org.
Different roles. I could have agreed if you said, say, PLOS. arXiv is a preprint repository, Elsevier publishes peer-reviewed journals.
The preprints on arxiv are read, and responded to, by plenty of peers. The question was what value Elsevier adds; I think the primary value added is just making papers available to anyone who wants to read them. Arxiv does that. (What's more, it does it for everyone, not just academics--as a taxpayer I can go on arxiv and read research that my tax money paid for. I can't do that with Elsevier published journals.) Publication in journals at this point is mainly resume padding and status signaling, not an actual value add.