i think the easy answer is start all pts on the 4 (or 5) drug regimen and simply stop whatever component a pt can't tolerate adn get some of the efficacy value of the added drug even if a full course of that drug is not taken
in the real world though it may not be that simple - there can be overlapping SEs so you don't know exactly which drug to stop, if you happen to stop a DAA early when in fact it is say interferon causing the SE you could get resistance to that drug in future if dont get a cure, some pts may just not want to feel like the have a flu for even a short period of time and may opt out of interfeon up front, ...
but bottom line i agree soc will remain for some and perhaps many pts at least part of the mix even for a modest increase in efficacy