I may be wrong but I don't think people really solo MVPs much anymore as there is no real merit in doing so. With the @findparty/@registerparty command in place and as well as individual drop chances on Cboxes and Light of Icas being implemented, it is far more efficient to find a group to hunt with. The only time people would still really solo MVPs is when there is absolutely nobody hunting. Now, you mention that tanking is too easy and monotonous but that statement also applies to the DPS, like snipers. It is still the same, buff up and attack the boss and wait till it dies.
If we agree with the notion above that most people would prefer to group up rather than solo hunt (to save time and for efficiency) and let's say that champions got this change so that steel is now 15 seconds - if I am a person who wants to dual log, I would still dual log with a priest + champ and just buff myself and focus on my champ tanking. Or If I am one of the archer dps, I'd still dual log with archer +another support. The changes on champ will not have accomplished anything. Dual loggers would still dual log. The proposed changes to champ only serve to handicap solo players who want to dual log but doesn't do much for those who decide to party up.
I think there probably exists a method more ideal to combat dual logging. Steel body and the way MVPs are hunted at the moment, in my opinion, does not have too much issues. I just genuinely think there is no real need for changes on steel body. I could definitely be wrong but these are just my current thoughts on Steel Body and the dual logging situation.