currently, no. 1.2.1 only supports original GB games, but 2.0.0 should support GBC-enhanced games. I don't know if there will be a "GBA Studio" but I ... wouldn't count on it.
It will be playable on the GBA however the hardware of a GBA is very different then that of the GB, GBP and GBC. as a result a lot of the coding might actually need to be different and would require a completely different editor to run correctly.