Well, I am not sure if this makes sense. I think commercial providers could also do the HLV job. It requires no crew training, no special safety, no government in first place. Even if the only customer is the government.
The only commercial superheavy launcher that has some chance to see the launch pad in the near future is the Falcon Heavy. That remains far behind SLS in terms of sheer performances. Oh and to me Musk is not the Savior and I don't believe to some miraculous estimates about the costs.
If the US government wants his superlauncher, to me a strict derivative of STS (sidemount, inline Jupiter-style... you choose) would had more sense than the current SLS project. But... by now this is the way and I can only hope that in some way they will find the manner to flesh out the launch manifest that currently is fairly risible.
But the shuttle really needs its payload bay as work platform. Its not the best choice for simply getting cargo somewhere, but if you need to assemble a spacecraft or a space station, the Shuttle is really unique. So, it makes sense to have it - even if it is not the best choice for hauling cargo.
Maybe a lifting body version with a similar sized payload bay could be a better choice for exploration missions.
Here is the spaceplane evangelist that talk
I don't think that a Shuttle-like spacecraft is the only or the better choice if you want to assemble something in orbit. In fact, the entire design of the Shuttle was wrong in first place, precisely because of that gigantic and unusable cargo bay, dictated by DoD requirements.
Separation of cargo and crew is more rational in my understanding. A launcher without that rigid configuration, that can fly manned or unmanned as needed. A far, far smaller spaceplane for crew only. Automated and/or manned orbital tugs for the dirty work. And so on. A more scalable and modular approach.
And for BLEO exploration, I see the capsule yet beyond the spaceplane.