Could you put a free standing tub in the room. A picture of your space or a floor plan would help. I'm not sure about your wall ideas with regards to " I come to a standstill when considering what to use as a tub/shower surround as the planks will surround the shower enclosure. ". Post pictures to help others visualize.

There are 2 main kinds of vinyl plank floors. The ones that you glue down, and the more recent ones that are floating, clickable systems. Both types of floors have top layers of vinyl, and are waterproof. The clickable systems have special-made locking seams that keep the water from getting to the subfloor. The glue down kind is used all the time in both kitchens and bathrooms, and the clickable ones have been more recently as well. Karndean makes a beautiful glue down material, and their website should show you where theres a dealer. If not, depending on where you're located, we can help you with that. COREtec makes a great floating vinyl plank, and you can also find a dealer on their website. If you're anywhere near the Northeast, give us a call if you need assistance sourcing the material. https://theflooringblog.com/installing-coretec/ https://theflooringblog.com/water-resistant-flooring/ The Couture Floor Company

Click and float. If I had to glue it down, I would just do porcelain, since I'm pretty good at tile work (I just have soooo much more tile work to do) Why can't it go under cabinets? I would figure any expansion might be hindered, but could expand the other way (not a very large room, maybe 6' wide to the shower wall. The vanity is a RH furniture vanity, so the feed are on sliders anyway. Floor will take the weight, but with minimal contact area for any relative motion. Clawfoot tub is the same. Thanks all.

The material was indeed Marlite. Thanks to those who identified it prior to removal. It was applied directly to the original wood slats, which are about 1" thick. There also no insulation along the outside wall, which we're going to fix as we go through the bathroom. We're going to do a subway tile surround with dark grey grout and keep the original cast-iron tub. Here are some photos after we removed the old Marlite backing.