Mougeon et al. (2005) and De Garcia (2008) about contact situations and linguistic innovation. How best to demonstrate interference (intra-systemic transfer) (Mougeon et al.). What the relationship is between bilingualism and diglossia (De Garcia) (not the same thing, but related).
Bao (2004) on Lexifier Filter and Substrate Transfer, and the uniquely stable linguistic ecology here – insofar as these things are stable. Some challenges to Bao’s analysis based on the data, but the analysis can probably be extended and qualified, since LF and ST are constraints (ranked/violable). Interesting arguments about the consistency of productivity; the role of LF also would apply.