It's not out of the realm of possibility. I personally think that the odds are against it being true but, at the same time, we'll never really know for sure. What gives the idea that Bryan was always intended to be the main event at WrestleMania XXX some weight is the simple, 100% fact that both Vince and Triple H very much enjoy giving the collective internet wrestling community purple nurples from time to time. They've played internet fans like Hendrix played his Stratocaster in the past, they know just what to do or what to say to get under people's skins. Bryan is someone that fans genuinely wanna cheer for without being steered into it. They like him, they like his style, they like the energy, they like the fact that he's a "regular" guy with just the right amount of extraordinary without being over the top. They know how hard he's worked, how dedicated his is, how much he loves it and they don't particularly care that he's not some 250 pound Adonis. So seeing him get "screwed" over so repeatedly genuinely got under people's skins, including some of the hardest of hardcore smarks.
At the same time, if WWE did consider Bryan for the main event the entire time, they took a risky path to getting him there. A lot of wrestling fans can be fickle, a wrestler who was popular for a brief spell can find himself being booed or fans just generally losing interest in him. By taking Bryan out of the main event picture towards the end of the year, a we saw about this time last year, resulted in lousy buys for WWE ppvs and what may be the most lackluster feud for the WWE Championship in years: Randy Orton vs. Big Show. Thankfully, it was a short one but, nonetheless, it still resulted in lousy interest for a ppv.
WWE also kept Bryan out of the Royal Rumble match itself, and we all saw how that went down with fans hijacking the Rumble match itself once Punk was eliminated and once it was revealed that Daniel Bryan wasn't even in the match. You also have to consider what we know, or rather what we think we know, about Batista in that he's allegedly not somebody who enjoys playing second banana to wrestlers he thinks are inferior, and by inferior I mean smaller as he's criticized WWE's pushes of Bryan & CM Punk in the past. Batista was one of the biggest stars of the 2000s and one of the most dominant, so it's not at all illogical to think that Batista would only come back, even on a part time basis, unless he wouldn't be booked similarly. Plus, there are all the various reports alleging how unhappy Batista was with how he was being used since his return.
So yeah, while it's not impossible, I don't think it's all that likely. In my opinion, which is all it is, Vince McMahon seriously underestimated Daniel Bryan's popularity. Personally, I think it's a genuine example of Vince being out of touch with what fans want. I know it's something that Vince often gets accused of, but his underestimation of Bryan's popularity is an example that has some definite weight to it. Vince also thought that fans would be interested in a rehashed feud for the title, at the biggest show of the year no less, rather than seeing someone fresh, energetic and hadn't been so consistently pushed to the main event picture for years on end in the ways that Orton & Batista had. I think fan reaction to the Royal Rumble, Punk walking out and the immediate reaction to Batista winning the Rumble the next night on Raw finally got him to open his eyes; or to at least definitely reconsider. If that didn't, I think Bryan turning on Bray Wyatt on Raw in February and the MASSIVE reaction he got probably did.
They started hijacking way before Punk got eliminated. No one even cared that Punk was in the Rumble at that point.