Login.gov does not provide a sufficient level of identity assurance (IAL2 [1]) to serve as the IDP for this pilot and IRS functions in general (ID.me liveness check and facial recognition). IRS is working with Login.gov to upgrade Login.gov to deprecate ID.me for this purpose [2] [3].
Would it make sense to not proceed with this pilot until this was ready? Certainly not; Login.gov will catch up and meet IRS in the future as Direct File expands next filing season. Very similar to when Social Security Administration (ssa.gov) transitioned from ID.me and their internal IDP to Login.gov on September 18, 2021 [4].
(Login.gov partners with USPS to perform in person identity proofing for those who cannot perform remote proofing via a mobile device; a bar code is generated, which you print out or display on a mobile device for presentation to a USPS clerk with a government credential)
[1] https://pages.nist.gov/800-63-3-Implementation-Resources/63A...
[2] https://news.ycombinator.com/item?id=30430851
[3] https://fedscoop.com/irs-to-adopt-login-gov-as-user-authenti...
[4] https://faq.ssa.gov/en-US/Topic/article/KA-03217