[quote="mholt, post:24, topic:310, full:true"]
What kind of data are they going to mine? Let's Encrypt doesn't necessarily collect any valuable information from users.[/quote]
In this day and age all information is valuable.
I am not presuming that LE collects or shares data purposefully.
I do not know if it occurs or not but while IdenTrust is still the primary signer perhaps some traffic would hit their servers when customers hit the LE sites and view certs (at least they will see the name here if they dig a bit I understand) or when administrators set up LE signed servers. This is the sort of traffic that I suppose would give IdenTrust their moneys worth of market share data to justify the co-signing during the early days that LE is not registered everywhere by default. While it may not be much market data it would be a source that no other commercial CA is privy to.
I expect this will happen too but it does not increase IdenTrusts market share proportion, just the total market volume, however if users and administrators are happy with LE they may never go to IdenTrust or other CAs unless the LE service is in some ways inadequate (see thread on expiry periods). I expect that a lot of administrators will inevitably consider IdenTrust first if they are looking for a paid certificate and this may be the only benefit they need.