I think the only reason why it's taking so long is because that's how BMW are. They're fairly different to MB and Audi in that they don't offer all the variants of one range in a matter of weeks. You saw with the new S-class, within a matter of a couple of months the S65 hit the market.
BMW take it slow, not because they don't have the capabilities or resources to offer a full variant onslaught, but rather, release a few variants, and when those models reach a year or 2 in age, then other variants hit the market to provide an injection in sales, but more importantly, another opportunity to promote the series.
All the variants for the 4-door have hit the market now...so they've captured as many 4-door buyers as possible.. now they're gunning for those buyers who decided against the 4-door because it was a bit big for them. Also, buy offering a staggered variant release, it also gives rise to the prospect that some A3 and A/B class owners may want the newest thing on the market or could have been dissatisfied with their current cars and therefore are willing to try the new Baby-Beemer.
That's my take anyway
