Not only would you miss the purpose of the format, you would have to code in an entirely new ruleset into MTGO.
Interrupts, Mana Sources. Yeah, you're almost playing a different game.
That's actually not the issue, because most people who play Old School Magic play under modern rules, but with perhaps just a few tweaks (like errata on Chaos Orb and Winter Orb), or permitting mana burn.
Magic Online doesn't have Chaos Orb, so that's a problem. But Old School Magic is also about the aesthetic of the old cards. Playing Magic Online doesn't capture that. That's more of what I meant.