Do you know if dowels were set into the old slab before the new one was poured?
Why do you want to wet lay into thinset? With multiple distinct slabs and especially with those sweeeping curves, I would think that you need to be totally un-coupled from the substrate. Those slabs are essentially the same thing as a well compacted subgrade for laying pavers traditionally. I got curious and looked up “everblue pavers” (I’m a specs nerd) and their install manual is pretty clear that you absolutely can lay pavers into a light sand course over concrete (making appropriate considerations for drainage). If you go that route, you wont be glued down in thinset across any of the cold joints or expansion joints.
Those look like big 18” or 24” pavers. Uncoupled, I think you’re ok to lay a pattern across joints. My concern would be limited to vertical heaving, but that will be spread out across the length of the paver. You might ask the mfg if you should slightly increase the width of the sand joint to allow for a little more play. I don’t know how much you’ve increased the size of the existing pavement, but if its substantial I’d also think about waiting a season to allow the ground underneath time to adjust to the weight of the new slab and also equalize moisture content with the existing slab (clay soils in your area?). Next year you can come back and lay a level sand course across everything knowing that you’ve accounted for as much settling as you can stand to wait for. (I’d probably skip this if the slabs were doweled).
Personally, I’d think twice about a “tile approach” using thinset in this instance. Ditra does make a very specific outdoor uncoupling membrane that is designed for patios to be self draining, and somebody well versed in the product may be able to evaluate its potential here. That person isn’t me. Also, ARDEX makes great products. I really like them. Read up on the substrate moisture specs for the specific product you’re looking at using. When I was looking at using some last, I learned that some of them are designed to be used on green concrete. Others require a more substantially cured slab.
I assume you are working with a reputable local contractor who knows flat work and your region (not a Craigslist jack of all trades). Ask questions. Heed advice. Agree on a plan. You’re paying for experience.
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