I doubt you'll see more revenue from it. If you're low on v4 addresses and you're willing to put (some) subscribers behind CGNAT, then inplementing v6 should reduce the number of v4 addresses you need and thus reduce your costs.

If you give each subscriber an IPv4, then yeah, added operational cost, no revenue, maybe added capital cost depending on your equipment. Not much upside for a small ISP. In a competitive market, v6 can get you some points with the technical folks, but not many.

There's not much upside for a legacy network that already has all the IPv4 it needs, but an upstart ISP will do well starting with IPv6 and layering CGNAT IPv4 on top. With 30% of the Alexa top 500 supporting IPv6 (and a lot of the top traffic sites like Google/YouTube, Facebook/Instagram, Netflix etc) it will reduce the amount of IPv4 you need to buy

have you seen the cost of v4 recently?