The Prepatch usually lasts about 2 weeks. There are some who predict it might be a bit longer this time around.
I would really like to have at least 3 weeks for two reasons:
leveling belfs and Draenei paladins/shamans so they can catch up without having to forego social life.
have lvl 60 raiders enjoy Prepatch talents a bit longer. It’s a blast to raid with TBC talents and there’s such a small window to do it between expansions!
I would also like a longer pre patch.
They forget how many of us have real jobs and can’t power level to 58/60 in ~10 evenings.
I think that is an excellent idea, with 2 week prepatch there ain’t no way I’m levelling a space goat futa shaman, with 4 weeks+ I’d seriously consider it. Plus raiding with TBC talents is indeed fun iirc from 2021
I’d love it if it was 4+ weeks tbh. Pre patches always seem really stressful if you want the new race/class going into the new content imho. It’s not been such an issue with retail servers as there is normally an Bonus Exp event, which admittedly does do the job of levelling up very well, but doesn’t allow the slower paced gameplay of classic imho. I’d like to be able to maybe even do a raid or 2 before stepping into Outland, if I’m honest. 
I don’t get it why prepatch are this short these days, I did not play Classic 2019 and joined again when TBC came out. I do remember fondly that the Dark portal even was well over a month back on retail, same for Wrath of the Lich King in 2008.
I’d be for dropping pre-patch 30 days after Naxx. Then give us a couple of months to experience Ally Shaman and Horde Palas in the mix.
With so many R14’s the AQ content is already pretty trivialised to a level where guilds will mostly be entering in full BiS anyway
That would be Awesome tbh. A whole month of leveling and as you said even joining a raid or two before the portal.