The level limit for learning a grand master profession is still 75. If you have an alchemist, tailor, scribe, engineer or a gatherer, you will be able to obtain a skill of 525 without going past that level.
How does it work?
Basically, every city's trainers will let you train recipes that you can use to level (or craft for profit or whatever). The difference is that for these few specific professions, you will need to unlock your faction's area in Twilight Highlands to get access to recipes that have a higher minimum skill. Enchanting might actually still be able to get to the skill cap, because it looks like some of the trainable recipes are green all the way up. No such luck for the others, though.
First, this is all beta info. There's no way to know for a fact that this will be how things look at launch. That said, there have always been things you couldn't craft until you had your character in the endgame. In Wrath of the Lich King, this was accomplished by putting the recipes on raid bosses. The main difference here is that instead of having to raid to get these recipes, we will be able to get them for doing soloable content we likely would have done anyway on the way to 85. Blizzard still may put crafting perks in for the proper endgame, but obviously we don't see those yet.
The other difference between this and what we had in Wrath was that you could always get a large percent of functionality from your trade skill without having to be max level. It seems that Cataclysm is going to be putting much stricter limits on how much you can accomplish without putting your character through the content. For example, anyone with 415 skill, 5 gold, and access to a Northrend trainer can make an Eternal Belt Buckle. The Cataclysmic equivalent is the Ebonsteel Belt Buckle, which you will only be able to make if you have access to the vendor who sells the recipe.
Basically, now, instead of having a very small portion of the potential of your trade skill "locked" to raiding-only characters, we have a very large portion of a few skills locked to "non-alt" characters.
How will this affect me?
Depending on how you use professions, this may or may not be a big deal to you. There are two camps: those who want to have access to each profession (possible for auctioneering), and those who mostly use a profession for its endgame benefits. If you're in the second camp, when you get to the Twilight Highlands, you'll be set. If, however, you're trying to build a "stable" of alts with a variety of professions, this is bad news -- unless you're doing it for completionist reasons, of course. Completionists like to have all their characters at the maximum level, anyway.
Gone are the days when anyone could get away with a couple of max-level-minus-15 characters on an account to use to increase the available professions he had access to. Now, you need to level every single one of them to almost the level cap. This is going to have an effect on supply of crafted goods; the fewer people who can make something you need and can't make yourself, the more margin they'll charge when they sell it. This means more of your hard-earned gold will be going to people who have time to grind alts to level 84.
If you want to capitalize on this, the obvious method would be to get your characters to 84 as soon as possible so you can be among the few people who have the ability to make the crafted goods that become available then. Also, take advantage of the new guild interface and work cooperatively with friends, if you can. Avoiding having three people in the same guild hit 525 blacksmithing at the same time reduces the duplication of labor, to say nothing of competing for raw mats. Still, there's no way to take a shortcut around this. A huge portion of the popular crafted goods for a couple of important trade skills are locked behind several weeks to months of leveling per character.
Insider Trader takes you behind the scenes of the bustling subculture of professional craftsmen, examining the profitable, the tragically lacking and the methods behind the madness.