I'm assuming @baimafeima is talking about certificate generation in particular, which I would also like to see. The official client is CertBot, but given that the Solus Devs like Go, there is also acmetool (these are also two of the tools mentioned in the above openSUSE article). Certbot is in multiple distributions' core repositories while acmetool has third party repos or build scripts available for multiple distros and is packaged in the Void Linux core repos.
This will most likely turn into a package request for CertBot or another ACME client, but maybe the devs want to decide which client is best to use, or if multiple should be included? Here's a list of clients sorted by programming language
Can't you just sudo pip install letsencrypt ? I mean sure we could package it up too - I'm just sorta failing to see where its needed for Solus. You're not really running public Solus servers now are you :P
For my own personal use case, it would be to generate certificates for my websites on the shared server I pay for. They do not have integrated support for Let's Encrypt so I have to run the client from my personal machine and upload the generated certificate to the server. I could download the standalone version, but having it available as a system package means automatically getting updates - updates to Certbot seem to occur about once every two weeks.