How many merits? The devs have datamined how long it takes people to run the regular arcs and based the merits off of that, they don't have that information on the dev choice arcs.
My arcs are constantly shifting, just search for GadgetDon for the latest.
The world beware! I've started a blog
GadgetMania Under Attack: The Digg Lockout
Synapse told me in a PM that they are considering the option of adding merit rewards at some future date. No firm promises though. In addition to the datamining aspect I think they wanted to make sure they understood how merits and tickets balance out against each other before making that change. (That last bit is me hypothesizing, all Synapse said was they were considering it.)
And for a while things were cold,
They were scared down in their holes
The forest that once was green
Was colored black by those killing machines
if a dev's choice arc gives same rewards as a real mish arc, they should give reward merits as well.