Does this sound grotesquely un-AC/DCish to you? Be truthful, Jake! It's Malcolm's nephew Stevie stepping in for him (due to Malcolm's alcoholism) on the 1988 tour. If you had been there that night you wouldn't have had a better view and if no one would have told you beforehand you would not have noticed but cheered on.
Let's face it: 90% of the people in those stadiums didn't care or didn't know and did not realize. They wouldn't recognize Malcolm Young on the street. To them AC/DC is the music (his music, granted) and the two frontmen, Angus and Brian.
KK Downing's lead and rhythm playing as well as his "Flying V and leather, blond mane"-look were instrumental (no pun intended) to Judas Priest's sound and image, he was also a major songwriter, but Priest didn't really miss a step replacing him. Yes, a few true believers miss him, everyone else likes the youthful enthusiasm and easy attitude of the new guy. And, yes, I do hear the difference when Roger Glover is ad hoc replaced in, uhum, "that band that isn't as popular as the Sex Pistols" one day ahead of a gig due to a bad arm and they get some talented finger player in and it mars the DP experience for me, but would you care or 90% of the people who came to hear Smoke on the water?
I can understand the grief of Malcolm's bandmates about him not being able to play anymore, but AC/DC will not be selling one ticket less if they tour with someone credible taking his place. With all due respect, I believe there are a handful guitarists out there who can ape Malcolm's rhythm playing well enough to sustain the illusion for the regular concert goer. Very few instrumentalists are really irreplaceable in rock bands when it comes to live performances.