You mean sort of a Roman soldier or gladiator inspired gimmick? It's something that MIGHT have worked 20-25 years ago, but it'd be ridiculed with hedonistic abandoned by too many fans today. Many of today's fans are too smarky, too jaded for their own good to suspend disbelief over much of wrestling itself these days, so they'd absolutely rip into this without remotely giving it a chance.
One reason why the Undertaker continues to thrive is nostalgia, he's also someone that's really respected by a lot of fans. If you tried to debut Taker's gimmick in some fashion today with some guy in his mid to late 30s, there'd be fans who'd all but laugh him out of the ring no matter how big, strong, athletic or intimidating he was. They'd crucify Roman Reigns and blast WWE mercilessly for doing something like this partially because it does sound a bit goofy when you get right down to it in this day and age, and, partially, because there are fans who're gonna crap all over Roman Reigns no matter what; they've decided to dislike the guy regardless of what happens from here on in.
I'm of the opinion WWE's best shot for Reigns is to turn him heel and go full out, badass heel with him. Don't try to make him cute, don't try to make him witty, don't give him one liners or catchphrases to taunt the fans with; just go the route of making him a vicious, ass kicking savage with no remorse for anyone. Would it work? For some, I've no doubt but, as I said earlier, there are some who'll hate Reigns out of principle. Another problem is that sort of character, for all intents and purposes, sounds a lot like Brock Lesnar where Lesnar had the advantage of some nostalgia himself, due to many fans still fawning over his roughly 2 year run back in the 2000s, and establishing himself as a legit badass in his MMA career. While said career's greatness has been heavily inflated in WWE, Lesnar did draw a helluva lot of money, he did win the UFC Heavyweight Championship and he did defeat a respected & beloved MMA legend in the process. Lesnar also has Paul Heyman doing his talking for him and Heyman does a masterful job of constantly hyping Lesnar in a passionate way. I don't know if WWE would be able to duplicate that sort of success and would probably be criticized if they did try that same formula with Reigns. Maybe if they kept his mic time short & sweet, kept the intensity up and he looked like a savage during matches & beatdowns, it might work. All I can say for certain is that it's not gonna happen with Reigns using the formula they have now.