Slides will contain appliances, etc or interior access will be more limited for most layouts. Weight and potential connection issues due to movement vs space are tradeoffs but if you want the additional space I just don't see any way to avoid appliances in a slide.
My kitchen slide might be an extreme example as it contains water, drain, propane, 2 120V circuits, numerous 12V wires including 2 light circuits, switches. Plus I added 2 wires.
The design is interesting: All of the wiring and plumbing is configured as a sideways U shape with the bottom leg secured to the main floor and the top leg secured to the slide and moves in and out. Everything on the U is super flexible material and hence there are 2 connections for every item on the U. ie The wiring/plumbing material on the U is not the same as the rest of the rig. Multi small stranded copper flexible wiring for example.
So yes there is flexing and additional connections. And the access is limited and on one side. I've opened a cabinet side for unrelated wiring access (I hate exposed wiring) and if necessary I could cut out the back of the bathroom cabinet for access to the third size.
Definitely tradeoffs for the floor space but one that I wanted to make.