I think it will be the best shopping cart on the market.
It already has some pretty impressive competition, both open source and commercial within the ecommerce marketplace, so it's going to take a while to get established and start taking business from the other software vendors. It is only going to seek out new customers outside of the existing Coffeecup customer base, if it is marketed far more proactively by the Coffeecup team, than the current basic version. The fact that many of us only stumbled on the current version by fluke or sheer chance, speaks volumes.
Where the pro version really differentiates itself from the other ecommerce offerings, is that it has been developed on direct feedback from folks that actually use shopping carts in real world situations, rather than a developer's idea of what they 'think' online trading is all about. This means that the pro version will be infinitely more practical than many of the overburdened and difficult to use solutions that already exist out there. That will ultimately make the world of ecommerce far more accessible for many small to medium enterprises.