Did you meet with your designer?

Looking forward to hearing what she says. I had one further thought, if you're adding the doorway from the kitchen to the mudroom, could you close off the entry from dining room to mudroom? Then you could use that wall for pantry storage.

I don’t think that’s a great solution. Here are the recommended clearances behind seating:
36" if there's nothing behind the seats other than a wall and it's not a path through the Kitchen
44" for seats with a traffic path behind them but no appliances, workspace, or similar.
51" to 54" if there is workspace, appliances, or similar behind the seats. You of course don’t need to follow these recommendations, but you’ll want to make sure you’re aware of them and I don’t think it’s a great idea to have an island that doesn’t follow more than one of them.