MP 19 (Smokescreen) came out in December

So we have for 2014...
MP 12G (Gen2 Sideswipe) in February
MP 13B (Soundblaster w/ Ratbat) in March
.
then a five month gap
.
MP 20 (Wheeljack) in August
MP 21 (Bumblebee)
MP 22 (allegedly Ultra Magnus)

Since the previous Cassette 2-packs had their own numbers, and we have 19, 20, 21 & 22 noted for this year as Autobots, it doesn't leave much hope for any more cassette 2-packs... or any hope of a Hasbro release of Soundblaster with 5 cassettes (if there was any interest by Hasbro to do one).
With Soundwave being so successful, I'd imagine Soundblaster would be high on the Hasbro agenda, as they managed to successfully sell a "green Starscream" that wasn't even a Gen1 character, so shouldn't have much trouble selling a black Soundwave (who was at least a Gen1 character, just not in America).