Your existing Alchemy will continue to work, right up until it doesn't. When that happens it'll be Microsoft's fault, not Apple's.
Of course, you'll not be able to buy any expansion libraries for it, because Apple doesn't allow such practices. Just try to buy a $3 generic charger cable for your iPhone...doesn't exist, because the connector is patented and Apple thinks it's entirely reasonable to charge $20 for a foot-long cable.
Logic users should not feel too smug about this. Apple could very well decide to abandon the product entirely - it wouldn't be the first time.
Alchemy never moved from my wish-list to my buy-immediately list, so I'm not out anything. But it makes you wonder what other mom 'n pop software companies Apple's gonna gobble up next.