It would be more of a surprise for United to express an interest in a new stadium because no matter how 'modern' and 'ground-breaking' the design for Liverpool's new stadium is the main reason for it is the increased capacity.
More people = more money
We already have a stadium with a capacity of 76000 and there is the scope to increase the capacity to 100000.
I think fans were more worried that under the Glazers we'd end up renaming Old Trafford as The McDonalds Stadium or Microsoft Stadium or something!