I have to be honest, I’ve never seen the suggestion that it was Petra (as what we know of the history of Petraean settlement wouldn’t support the dating), but that the original “Mecca” was somewhere in northwest Arabia south of it…somewhere.
The theory has wheels mainly from the source criticism of Patricia Crone, in her book Meccan Trade and the Rise of Islam, and it hinges on things that are not easily dismissed by naysayers: the setting described in the text of the Qur’an doesn’t match the geographical location of Makkah (I’ll use the official English spelling the Saudis use to differentiate between the city known by the name currently, and the Mecca of the prophet’s time—hypothetical Mecca, if you will); Mecca is described as having fruits and plants and animals that do not exist in the environment of Makkah; and, for its supposed status as a major trading center in western Arabia, Mecca is described in no non-Arabian texts from the late antique period (nor really even all that well in texts from Arabia). Crone theorized that, since Gaza is much more prevalent in descriptions of trade than Yemen (Makkah being relatively in the middle, so one would expect that travelers would be going in both directions with the same frequency), Mecca must have been located closer to Gaza, further up the coast, and in a much more fertile environment.
The theory is given a boost (or, rather, not easily disproved) due to the Saudi government’s reluctance to allow foreign archaeologists to work in the country, especially on sites related to early Islam, so it’s not like archaeological teams can go out and scour the Hijazi desert looking for clues to prove it or disprove it. And epigraphical (textual) expeditions led by Ahmad al-Jallad (Ohio State) seem to suggest that the dialect of Arabic recorded in the Qur’an may have origins in what is now eastern Jordan/northwestern Saudi Arabia, rather than in the Hijaz as was long believed to be the case.
So, in other words, as crazy as it sounds to suggest that Mecca—the setting of the drama of early Islam, which is mapped onto real, physical locations that once existed but have been erased by the Saudi government’s hyper development of Makkah (for details, see Rosie Bsheer’s excellent Archive Wars)—may actually have occurred somewhere else … isn’t as implausible as it seems. And it’s worked its way into scholarship as a possibility — not always a definite fact but at least a possibility.
But.
The flip side to all of the above is that it would have required some sort of combination of massive amnesia and conspiracy to somehow convince people that the historical Mecca was unimportant and replace it with Makkah, which would have had to happen sometime within the first few decades of Islam because there are (were) sites that dated to the mid-Umayyad period in Makkah, as well as waystops on the pilgrimage route that only make sense if they’re heading in the direction of Makkah.
And, as much as I can clearly articulate the reasons why there are some plausible questions about where Mecca was … I find it very hard to wrap my head around how and why the early Muslims — many of whom knew the prophet or early Muslims and/or were descended from them — would have agreed to somehow swap the epicenter of the Islamic cosmological universe for a completely different place and never mention it.
We have early copies of the Qur’an. We see minor textual changes (usually pronouns and things like that—I to we, that sort of thing), so that we can now pretty solidly and with textual evidence verify that the basic frame of the Qur’an, as we know it today, was largely in place by the mid 7th century, around the time we believe the prophet Muhammad lived. Like … even though it’s claimed that the caliph Uthman ordered everyone to wipe out all non-conformist versions of the Qur’an, we still have these versions that aren’t a 100% match … so where are all the edicts ordering the change in the qibla (the direction of prayer) from Mecca to Makkah? And are we to understand that everyone just said “okie dokie” and went along, and there were no holdouts whose erroneous qiblas left traces to be discovered by archaeologists working in early Islamic sites in the Levant, Iraq, Egypt, Iran?
I’m ranting a little bit, apologies. I think where I’m going with this is that there’s a lot of attention on the idea that Mecca could have been somewhere else, but there hasn’t been a correlating effort to demonstrate that Mecca could have been Makkah. For example: the city probably only had a permanent population of about 5,000 at the time of the Prophet—that would have been big for the arid, water scarce Hijaz, but not that big in the grand scheme of things globally. Is it not equally plausible that the early Arabs, in describing Mecca as a large trading center, were describing it in an Arabian context?
Another thing that comes up is that there was a cooling period in the eastern Mediterranean in the late 500s. Is it possible that the reason that the Qur’anic descriptions of Mecca don’t match up with contemporary Makkah, but that they might have accurately described a slightly cooler, wetter Hijaz that only lasted around a century before it dried up? (One of the reasons that the capital was moved to Damascus was that Madina was bursting at the seams—and they were running out of water.)
So … the tl;dr is this: the idea that Mecca was somewhere up in Northwest Arabia isn’t as far-fetched as it may seem. However, I also would argue that there hasn’t been a substantial counter effort to determine whether it’s possible that Mecca and Makkah are the same place — it seems a lot like some scholars are more interested in playing with the shiny new theory than they are giving a critical lens to the old one.