"Whether we'll see 15K 2.5-inch drives is a moot point"
You mean like Seagate's Savvio 15K and 15K.2 lineup?
While coping with the executive disarray of changing its CEO and COO, Seagate has also found time to announce a couple of new disk drives - a 600GB Cheetah 15,000rpm drive along with a new 10,000rpm version. Cheetah drives are Seagate's mainstream 3.5in business drives, spinning at 10,000rpm (10k) and 15,000rpm (15k), compared …
I have no idea (I hadn't come across the concept before). It's reasonable to expect the same sort of tricks being played by those desperate to eke out the last drops of performance with 2.5" media as with 3.5" media. Though since you can get about twice as many 2.5" drives in the same space as previously occupied by the 3.5" drives, it's probably needed less, and the benefit will be less anyway (smaller platters mean less of a difference in speed across the platter). The cost differential between SSD and HDD for equivalent capacity is going to take a while to disappear, IMHO.