(via The Hollywood Reporter)
On top of all the LEGO Movie sequels that have been planned for the rest of this decade as well as a Ninjago spinoff, Warner Bros. is now developing another installment of the franchise by giving the LEGO Batman character his own spin-off movie.
Also, to answer your question, yes, it will be voiced by Will Arnett.
There’s no doubting this is a smart move for Warner Bros. since the original LEGO Movie was a critical and box office smash hit. Note that, by 2019, according to their plans, Warner Bros. will have made and released 6 films under the LEGO Movie franchise.