It will be possible to craft Mythic equipment for raiding
For items of quality, the equipment that is equipped will be able to have five different quality levels WoTLK Gold, for consumables like potions will have three. Each level of quality increases the effectiveness of an item in a small way, with Blizzard declaring that the aim that the program aims to "have the level of quality that is sufficient for it to warrant the effort to reach higher levels while ensuring that the benefits won't to be so huge that the most basic versions do not feel worth the effort." For gear, more expensive products will have a higher value item, whereas high quality consumables can have longer durations or additional uses.
Crafting recipes are a issue and the quality of the end product being crafted is determined by the professional's basic skill as well as the quality of reagents including special finishing reagents, equipment for professions that can give special skill bonuses, bonuses that are derived from consumables, and specialty areas for a particular profession. There's also a little chance of randomness in crafting, which could make result in the product being superior, or worse than what you would expect. A new stat in crafting, Inspiration, could grant more skill-based bonuses while crafting additionally, there are statistics that can allow made-to-order items to use up less resources, and also to create more items, and boost crafting speed.
Blizzard promises that it will be possible to craft Mythic equipment for raiding (aka the best gear available in the game) via this crafting mechanism, but it's likely to be a challenge. To do so the player will need to become an expert in the type of gear being made to acquire the top equipment and reagents required, including top-of-the-line optional reagents, and make use of the top equipment for professionals available. In the process, they may need to get a little lucky with an Inspiration proc or use a special finishing reagent to further boost the equipment to ensure it is made at the top quality.
There's a wealth of information in the entire blog post, including that players buy WoTLK Classic Gold have to increase their professions to the point where they will be in a position to learn all crafting recipes to their profession and that a new form of consumable called Phials will be replacing Flasks.