No, I don't think Disneyland as we know it would be built today if it didn't already exist.
Walt Disney Productions had some unusual circumstances going for it. The creative guy had his name on the studio. The financial guy was his brother. Walt had to rent out his own name to the studio in order to finance the project. When he asked for "too much" money, it caused tensions between him and the shareholders. Roy went to bat for his brother even when the two severely disagreed.
I think a park of Disneyland-level innovation and originality could be successful today, but I don't know that any of the current big corporations will attempt it anytime soon. (At least not in the U.S.)
Some things about the market were different back then, too. For one thing, there were only three major TV networks. When Walt came on TV to explain his new theme park projects, I imagine it was to a much larger portion of the viewing public than it would be today. However, this shouldn't mean that it's "impossible." A film studio promoting a theme park using a TV show was a new idea at the time. Find new ways of promoting and profiting from original theme park attractions now! Be creative! Original video games are promoted like movies these days, with trailers - why not promote original theme park rides this way?
Every time I see a new "theme park" announced, it's usually a coaster park. I remember seeing something about a rock 'n' roll themed park online. Sounded really cool. So I looked it up and what did I see? A few mildly themed looking buildings surrounded by garishly painted steel tracks. Nothing wrong with that, but to me, it's not a true theme park.
The only thing I see that even looks like its trying to compete with Disney here in the U.S. is Islands of Adventure. And even that has Exposed Steel Syndrome.
It does surprise me that there isn't some eccentric billionaire who is a Disney fan and wants to build his or her own theme park.
I sometimes wonder what would have happened if Pixar had split from Disney and eventually went on to expand into it's own Disney-like studio, distributing their own films, with a live action division, theme park division, etc. But that doesn't seem to happen too often today. Despite being founded by three of the most major moguls in Hollywood, DreamWorks films are still being distrubuted by other studios (did they ever have their own distribution?), while Shrek resides at Universal Studios theme parks.