Sorry John, Just getting back to it now. Thanks for the offer. I may call you this week if needed. Looks like if I remove the floor in the shower and lower it down to being flush with the joists and double up on the 5/8" thickness then I'll have a good solid floor to build up on. Looks like Schluter linear drain is about 1 1/8" to top of drain / kerdi weatherproofing point meaning I would start tiling from that height above the joist top.
If I add 3/8" plywood on top of the 5/8" osb that is currently on the rest of the floor then floor heating and Ditra then I should be about 1 3/8" above top of floor joists when I start to tile in the bathroom. So with about a 1' of slope from bathroom floor to drain then I'd make up the 1/4" difference in height.
Does this seem to make sense to you? I assume all other linear drains are similar in dimension and mud requirements.
Finished floor height would then be 1.75" above joists. When I redo bedroom floor to hardwood then it would be about 1.5" about floor joists. That should be good for mating with new bathroom floor easily.