Shadowprotect 5 also allows the consolidated monthlies to be merged together which is a substantial improvement.
Also of note is that upgrades from version 4 to version 5 will require rebuilding the backup chain.
On another note, I posted this question two months ago and bumped it twice. A simple "we don't know yet but will respond as soon as we begin testing it" would have been greatly appreciated. Being kept in the dark about major product releases from Storagecraft will only motivate us to buy directly from the vendor in the future.