I tried the same thoughts about avoiding a duck-under but trying to have a reachable table width with two STD dog bones at each end just eats up too much real estate to allow any space for O gauge tracks in the middle and still have some scenery space. I ended up having one section of pure tinplate village of about 5'x8' with the fun tinplate buildings and 42" / 57" curves with switches, etc.
Then from that, the longer outside 72" loop around O gauge tracks is manageable with a duck under (hinged to lift up). Great modular sections by Sievers was base with plywood and Homasote for noise reduction. Two loops of O gauge can fit in the middle of STD gauge with some room for spurs.
I think you will be sorry by trying to cram all the O gauge track in the middle of smaller STD gauge loops. too much compromise.