With half of the web using Let's Encrypt certificates, I think it's pretty safe to assume the intermediates are in most users' caches. If you get charged out the ass for network bandwidth (i.e. you use Amazon/GCP/Azure) then you may be able to get away with shortened chains as long as you use a common CA setup. It's a hell of a footgun and will be a massive pain to debug, but it's possible as a traffic shaving measure if you don't care about serving clients that have just installed a new copy of their OS.
There are other ways you can try to optimise the certificate chain, though. For instance, you can pick a CA that uses ECC rather than RSA to make use of the much shorter key sizes. Entrust has one, I believe. Even if the root CA has an RSA key, they may still have ECC intermediates you can use.
