What I am proposing is simpler. Just allow for turning off the preamp in an amp block. we can already turn off amp modeling. It would be running 2 amps in a series, the first with preamp on and amp modeling off, and the second would be preamp off, and amp modeling on.
The above thread seems to try to address real world situations of using the send/return of different amps to bypass preamp or power amp stages.