It hasn't reached "obsolete" status because it still gets used in historical contexts; thus it should probably be labeled "archaic"; to wit:

John Madden's last film was Mrs. Brown, in which he deployed the relationship of Queen Victoria and John Brown with stateliness and wit. Here he has seemingly swilled some of Falstaff s sack and has had robustious, fiery fun. Judi Dench, who was his Victoria, is Elizabeth here, and no one else could be tolerated in the part. Madden's most impressive achievement, amidst all the hurly-burly, is an intimate, almost internal one.
- Stanley Kauffmann; The New Republic, Washington; Jan 4-Jan 11, 1999

or,

Either actors "speak the speech . trippingly" while "us[ing] all gently... with temperance" and "smoothness," or they "mouth it" like a "robustious fellow" while "saw[ing] the air," "strutt[ing] and bellow[ing] (Hamlet 3.2.1-33). In his account, timing joins such theatrical elements as intonation ("accent"), bodily configuration ("robustious"), and behavior ("gait") in being correlated with an offstage social polarity that opposes the "barren and incapable" to the "judicious."
- Shakespeare Studies; Columbia; 2001; James R Siemon

The silent pirates of the shore
Eat and sleep soft, and pocket more
Than any red robustious ranger
Who picks his farthings hot from danger.
-RLS