it would be rather easy to write in black panther.
you could list wakanda as the source for vibranium used to possibly build ultron.
that fails, before ultron is created.
plus it could show the origins.
entailing past failed super soldier serum experiments.
that failed trying to emulate the famed of the spirit of wakanda's the black panther.
plus the origin of cap's shield. as the only salvageable thing from the failed mission.
to synthesize the super soldier serum using the original bp as a template.
black panther, antman and iron man need to be in the avengers if it goes further.
as you can have no avengers without ultron.
plus if they have vision then they can have black panther.
as you need the collective intelligence in unison of bp, antman and iron man.
to combat ultron's desire and cunning use of intel and ai.
so bp will have to be introduced. bp could he introduced for an avengers/xmen crossover as well. as i think wolvie was in wakanda in the origin movie if i remember right.
so, you could cite box office draw receipts for the wolvie orgin.
to justify, why it is a good choice for a marvel movie.
imo, idris elba should be the guy used for black panther.
the avengers are not traveling to asgard in the movies anytime, soon.
art barr