There has been no end of sale announcement for the SCA, so there is no way of knowing when (or if) it would be phased out. Since the SCA is really another's company's relabeled product (SonicWall), it would also depend on that company's future plans for the product.
The SCA is a good alternative for people not using the CSS11500, or who require functionality offered by the SCA that is not offered by the CSS11500 SSL module.
In addition to the the CSS SSL Module and the SCA, another alternative would be the Catalyst SSL module.
