The DVD Forum is not very powerful, period, first of all. They established the DVD format, and basically nothing at all since then. They accomplished nothing with recordable DVDs; witness the + and - versions, which are basically equal in the market (or maybe + is a bit ahead, having had DL discs available first). The forum's HD disc format has now failed, and there is probably nothing else the DVD Forum can decide or promote that will carry any weight in the home-entertainment business. For example, if the Apple or Microsoft HD download systems started to gain real market share in a few years, like 10-20% of rental revenue for either, but then the DVD Forum came out with a different system even with some big partners, do you think the MS/Apple one would just shrink away then? Since there is no "power" there, the BDA has nothing to take over from the DVD Forum.
If you are just asking whether BD will eventually sell more copies then the same title on DVD, that is a different question, but is not related to 'BDA versus DVD Forum'.