Even sites with that option already (like wikipedia) still report being hammered by scrapers. It's the full-funded aligned with the incompetent at work here.
replyIA has always been in legal jeopardy without offering paid access. For that to work we need to get rid of copyright first.
replyOr offer it in countries with lax copyright. The industry will find ways to work around it.
replyBut - as another poster pointed out - Wikipedia offers this, and still gets hammered by scrapers. Why buy when free, I guess?