Johnson v. United States, 135 S. Ct. 2251 (2015), strongly supports the argument that 18 U.S.C. 16(b) is unconstitutionally vague. The question remains, however, whether the Board of Immigration Appeals (as distinct from a federal court) has authority to find 16(b) to be unconstitutionally vague. Sejal Zota's practice advisory offers a nonconstitutional argument to get rid of BIA's endorsement of ordinary case rule struck down in Johnson.
http://nationalimmigrationproject.org/legalresources/practice_advisories...

Thanks to Ben Winograd.

Comment: In prior cases, the Board has declined to consider such challenges under the general rule that it lacks authority to strike down a statute or regulation as unconstitutional. See, e.g., Matter of G-K-, 26 I&N Dec. 88, 96-97 (BIA 2013). While the Board might lack authority to strike down a statute as unconstitutional in the first instance, it arguably possesses authority to consider the constitutionality of a statue under a controlling decision by a circuit court or the Supreme Court. In other words, while the Board itself can't find a statute to be unconstitutional, it can find a statute to be unconstitutional under the ruling of a higher court. Matter of Silva, 16 I&N Dec. 26 (BIA 1976), may support this argument. In that case, the Board held that 212(c) waivers are always available in deportation proceedings to avoid the equal protection problems that the Second Circuit identified in Francis v. INS, 532 F.2d 268 (2d Cir. 1976). See also, Matter of Fuentes-Campos, 21 I&N Dec 905, 912 (BIA 1997) (We recognize the canon of statutory interpretation stating that constructions of doubtful constitutional validity should be avoided where possible. See United States v. Witkovich, 353 U.S. 194, 199 (1957); United States ex rel. Attorney General v. Delaware & Hudson Co., 213 U.S. 366, 407 (1909). However, inasmuch as we find no ambiguity in section 440(d), we find it unnecessary to resort to this canon.); Matter of Abdelghany 26 I&N Dec.254 (BIA 2014) (We would face an obstacle to adopting the Abebe approach as a nationwide administrative rule, even if the regulations permitted us to, because that approach may well conflict with the Second Circuits constitutional rulings in Blake v. Carbone and Francis v. INS. Because the Second Circuit has already held that denial of section 212(c) relief would pose serious constitutional problems for deportable lawful permanent residents whose offenses are encompassed by the grounds of inadmissibility, we arguably are not free to adopt FAIRs proposed interpretation in Second Circuit cases. Cf. Edward J. DeBartolo Corp. v. Fla. Gulf Coast Bldg. & Constr. Trades Council, 485 U.S. 568, 575"78 (1988) (holding that the imperative of constitutional avoidance trumps traditional principles of administrative deference).).

Thanks to Dan Kesselbrenner and Jonathan Moore.