Currently, there’s no information on the adoption rate of different ACME clients. Adding a chart of the prevalence of different User-Agent headers seen in calls to the ACME API would be a nice statistic to add to the statistics page.
The code generating the statistics page doesn’t appear to be published, so I don’t know how difficult this would be.
This information would also have a small operational advantage: knowing what clients, and what client versions, are in use allows decisions to better be made whenever breaking changes are made to the ACME protocol. Although rare, the ACME protocol has yet to be finalised and there has already been a transition from the “simpleHttp” and “dvsni” challenge types to http-01 and tls-sni-01, so such changes are not unprecedented.