I don't see the point in making M&M X open world as there will be no innovation. The previous iterations and their user interfaces did very well to overcome the technology limitations at that time to make an open world game. Now we have much better technology, and better games were made using this technology (Oblivion, Skyrim, Fallouts) with companions. So I don't see the point of making an open world M&M game unless it competes with the existing open world games.
The new M&M X is used to exploit the current nostalga and boom in 'old school' rpgs, not to innovate on what has been done in the past. Therefore they are correct and would expect them to make a linear game along the lines of Grimrock.