One of the key lessons learned in the past half-century is that lawsuits like that are:
(a) Often won
(b) Pyrrhic victories
Right now, it's the policy of Paramount not to sue over very clear violations of Star Trek copyrights (see: Star Trek Continues), Rowling to not do the same for Harry Potter (see: Methods of Rationality), etc.
A lawsuit like that results in a modest payout and take-down, together with a loss of brand worth many times that.
On the other hand, the derivative works tend to drive brand value, recognition, and sales.
That's why many works have clear guidelines supporting and encouraging derivative works, with specific boundaries to make sure they don't undermine those works.
I don't know The Sword of Shannara, but each time someone says "inspired by Tolkein" or "building on themes from," Tolkein increases in brand value as a classic and then THE classic. There is a legal line as to where inspiration becomes copying, but if we were to assume, arguendo, that it's clearly over that line, it still probably wouldn't make sense to sue. At best, that would have a chilling impact on more works in the "inspired by" category.
(a) Often won
(b) Pyrrhic victories
Right now, it's the policy of Paramount not to sue over very clear violations of Star Trek copyrights (see: Star Trek Continues), Rowling to not do the same for Harry Potter (see: Methods of Rationality), etc.
A lawsuit like that results in a modest payout and take-down, together with a loss of brand worth many times that.
On the other hand, the derivative works tend to drive brand value, recognition, and sales.
That's why many works have clear guidelines supporting and encouraging derivative works, with specific boundaries to make sure they don't undermine those works.
I don't know The Sword of Shannara, but each time someone says "inspired by Tolkein" or "building on themes from," Tolkein increases in brand value as a classic and then THE classic. There is a legal line as to where inspiration becomes copying, but if we were to assume, arguendo, that it's clearly over that line, it still probably wouldn't make sense to sue. At best, that would have a chilling impact on more works in the "inspired by" category.