If we are looking at a new stadium I would personally like the interior of the stadium to look very similar to what we have now. Copy the North stand, East Stand, Stratford End and make the South stand just like the North stand for greater capacity. Also maybe raise the East Stand and stretford end higher to match the height of the north stand and new south stand and fill in the corners between all 4 stands. Keep the dugout the same. I am no engineer so no clue if this is feasible. Keeps Old Trafford feeling familiar but increase’s capacity significantly.
Then the concourse and exterior can be done up and modernised. The exterior keeping its red brick facade elements. I don’t want a glass bowl that a lot of modern grounds feel like. If we want to use the existing Old Trafford site afterwards maybe we keep the pitch location the exact same so we don’t lose that history but build a smaller stadium around it where the youth teams can play like City have done. Name it after Sir Matt or Jimmy Murphy, name a stand after Eric Harrison etc.