Photo would help. Only difficulty would be achieving the 2" lap required for Kerdi membrane floor to tie into the wall membrane.

Thanks Mike. That was my concern also. Any suggestions , ? liquid waterproofing or just using the kerdi as close as possible to the intact subway tile. Sorry about no photo will try and upload one soon

here is a photo but doesn't show the glass shower doors that are on the edge of the shower

I'd figure out a way to lay tile over the PVC.

Sorry. No easy way. I would want the new lap that seals to the wall membrane above the curb. Which would mean replacing the existing curb, removing & replacing a couple rows of wall tile. It's a difficult and risky undertaking. No guarantee the tile will come off the wall without damaging the Kerdi membrane. If it's Kerdi board forget it. The paper face will peel off. Sadly in this scenario your best hope is the wall tiles were installed poorly and that's not a good thing to hope for. I would research ways to refinish the existing base if possible. You never know what new products may be available. Sometimes there are options never considered.

https://www.labourmatters.com/teak-shower-floor/

I considered Joe C's thought. Flex in the base would need to be eliminated. Yep. thinking outside the box. Porcelain pavers on pedestals? You have my gears turning:)

https://www.google.com/search?source=univ&tbm=isch&q=pavers+on+pedestal+system&sa=X&ved=2ahUKEwiho8GCxbjvAhWYbs0KHYEQAmwQjJkEegQIFhAB&biw=1227&bih=567

Disclaimer - None of the above the above thoughts are approved methods:)

Joe C may have thoughts on how to solidify existing base. Spray in foam? Compressive strength?

There is existing perimeter support around base. you would just need center support for wood or porcelain.

jgweiser. You may cost me sleep tonight:)

Waiting for Joe C. to reach into his bag of tricks and come up with a solid surface solution. He's come up with some good ones over the years. Agree with Mint. Wood drop in would be my first choice.

I like the idea of ipe wood shower floor to hide the fiberglass pan and avoid the risk of screwing up the sides . Haven't done alot of work in this area so probably good advice not to mess up something and make it worse but the ipe wood might be nice. I can look into this . If i did go with the redo , couldn't i use the membrane with a liquid waterproofing solution or is that a bad idea.