The biggest deciding factor for everything is how much your willing to spend moving plumbing.
To some people with a smaller budgets(there are people of all income levels on this forum) jackhammering up the concrete to move the plumbing 20' could change the entire plan of their remodel while others with a bigger budget it might not be a problem. I dont know the going rate of moving plumbing in OP's location and would not be able to tell if it's a deal breaker or not and neither can you, OP asked for ideas, i was merely trying to relay the fact that moving plumbing may be something to consider in the budget, not "knowing" what their budget is or how far that money will go in there local area. Also you are straight up full of sh!t you dont know whether once they move the plumbing 30' if they will need to install a sump pump or whether the drains from the 70's are made of orangeburg pipe and the entire system needs replaced at the time of remodel so unless you have something to contribute i dont see why you want to push the point.
I am adding to the discussion. I am correcting misinformation. The fact is, plumbing isn't the biggest deciding factor. It's a factor, but hardly the biggest. I am not full of chit, because I do this for a living.
Now you are back pedaling and adding details to the scenario, but even then it doesn't change the fact that plumbing isn't the biggest deciding factor. When I work with budgets and clients I discuss all of their options. One of them is to do the project in phases. But the most important is to understand their budget. You made a statement without knowing his budget.
Another item that you discuss with a client is unforeseens. Since you cannot foresee a major plumbing, electric, structural...problem you do need to plan for that. I always put back 10% of the budget for these items. But you are right, sometimes an issue arises that requires a complete rethink of the project. But that is a very rare circumstance and is hardly one that can be properly planned for without a bottomless budget.
I know that people don't like their knowledge and information challenged, but I couldn't let that misinformation just hang out there for people to read for years to come.
For what it's worth, I do like you second layout, but haven't had time myself to sit down and play with his floor plan.