I don't even particularly like Luffy as far as MCs go (think he is SEVERLY overhyped) but Zoro would be to be rewritten and given a whole lot of background info to be viable as a replacement MC. His spare backstory and overall relevance work as an important character in Luffys story but if this was HIS story? It would never work.
If you just took most of Luffys past and transplanted it onto Zoro and tied it into his future role? Eh, maybe it can work. Make Kuina a Sabo-type figure, make Arashi into Dragon, Pinzoro into Garp etc but the reason a lot of people like him now would have to be utterly removed to make him being MC work. And before you say you are just remaking Luffy that is sorta the point. Oda has given Luffy the background lore and characters of importance appropriate for an MC while obviously not doing the same for Zoro since he ain't the MC.
Hell, he isn't even a member of the D. family line so whatever Oda has planned for that wouldn't work.
Now, if you were asking if Zoro could have been a better RIVAL than any of the supposed ones like Law and Kid? 1000% yes, easily. His background works perfectly for such a role I will argue to this day if Zoro remained a bounty hunter and clashed with Luffy and the crew every other arc or so that could have worked out well, even if it came at the cost of overall less Zoro than what we got.