If Disney builds a second tower and if it becomes part of the DVC (those are two pretty big IFs, by the way), it could be a taller structure than BLT. If so, it's top floors might still have a view of the MK.
As I've said before on the subject of a second tower, Disney would have to give the second tower some special appeal, or hook, to attract more DVC members and to generate an outbreak of addonitis. If a DVC member has already bought some BLT points, why would a second tower make that owner want to buy more points? And if a DVC member has not bought BLT by now, why would a second tower encourage them to do so? If anything, a second tower might have DVCers believe it will be easier to get rooms at the towers at the 7-month window, thereby lessening the appeal of having BLT as a home resort.
The feature that I would add to a second tower is a concierge level. AKV's concierge level has been extremely popular with DVC members. In addition, like the sunrise safari at AKV, I'd add a special cruise/boat ride on Seven Seas Lagoon for a sunset dinner and to watch the fireworks that is only available to BLT concierge level guests. With these "unique" features, some people might prefer the second tower.