I understand how you're currently looking at various interior
layouts and evaluating how they'll fit your needs. It really seems that anticipating changes to the layout is probably not all that productive. As others have mentioned, you'll find ways to use what's already there.
Truly anticipating future needs, with a sailboat, is extremely difficult to do. If you had years of ownership
and cruising experience it would be a different matter. Don't take this as condescension, okay?...it's not.
You might be glad you have a second cabin when you take another couple with your for a two week cruise
. Ditto for the head. That second cabin may be a good place to get away and work on your stamp collection, or play your guitar.
I would just counsel that having a layout that is somehow ideal or custom isn't really that important.
And, this is from a fussy guy who tends to modify and customize his stuff in search of perfection.
My two cents.