[tialaramex]

IdenTrust owns two newer roots which are widely trusted today, IdenTrust Commercial Root CA 1 and IdenTrust Public Sector Root CA 1 but they were only created in 2014.

Perhaps somebody has a list of what's in the trust store for various historical Android builds, I do not.

But I think you can assume that the team at Let's Encrypt have considered any options that might work and decided that either they wouldn't make enough difference to be worthwhile or have asked and been told it isn't possible or would be too expensive to make sense.