I thought about that card. I don't really need
additional ways to haste the drake - I'm often halfway through my deck when I wanna cast him, so I usually have at least one
Expedite by that time. However, it might be a good
replacement for 2 Expedites.
I would be very careful about replacing lands, though. With 21 you sometimes end up with 2 lands in your opener and you need both colours and double blue asap. If I was to include them, I'd just go up to 23 lands and drop 2 Expedites. The downside is that the Battlements don't cantrip and won't put an instant in the yard. With lots of card draw I often end up with too many lands already, so Expedite is to be preferred in many situations.
It's still a close call and certainly a good option, if you feel 21 lands are not enough.
Another card I'm not quite sure about is
Magma Spray. It's nice to have a permanent solution to some annoying creatures, but the difference between 2 and 3 damage is huge, so
Fiery Impulse might just be better in general. You don't encounter recursion every game, but you're almost certainly gonna have a use for additional points of damage. Even in the worst case scenario it still buys time by killing the stuff early on, and you can make up for the card disadvantage with draw spells by the time they can profitably recast their creatures from the yard.
Oh and while we're at it,
Kozilek's Return should probably be
Chandra, Flamecaller as the sweeper of choice. Hits for 4 when needed. Can hit for 3 and survive. Can replace your hand and get spells in the yard. Can be an alternate wincon. It's all upside unless your opponent managed to stick 2-3 creatures by turn 3-5 that are below 3 toughness, which is quite unlikely - and it's even more unlikely to have the singleton right then and there.
Replacing the whole hand is so powerful that it might be a good idea to swap
Exquisite Firecraft for
Collective Defiance aswell. Slightly worse against Planeswalkers, but other than that all upside. My first version of this deck had
Fateful Showdown for that effect, but it was a bit awkward at times with your combo pieces already in hand and a must answer threat on the board.
Collective Defiance making that effect optional is way better in this deck.
I made all those changes for now, to get a better feel for it. Running both Battlements in place of Expedites.