Maybe, If you are only selling MBs.
But if you are selling the whole product like an SFF computer, you will get a lot less hassle with customers screwing things up, if you just solder as much in as you can. That's just less for monkeys to mess up.
IMO there is 99.9%+ chance that any kind of big APU with more than 2 memory channels, will be solder in only.
This would be like Intel Kaby-G. You could only get it it soldered in. There was no socket option. Remember what a "big hit" that was.
It is not so easy to just solder things as people may expect, YES, it is cheaper and simplier than putting a slot and then adding a memory to it, in fact this is a lot cheaper and simplier.
But there are hidding costs. First off you need to decide how many boards to produce of each configuration AND DO NOT GET IT WRONG, if you get this wrong you lose a lot of money. And when you start adding variations the posible combination really start to get out of hand. Lets say, you have 3 possible socs, then you have 8, 16 and 32 gb of ram variations of each one, and finally storage, and you can see why storage is the last thing it gets soldered on, otherwise you would se EMMC used a lot more.
It was decided long ago that soldering the cpu to the boards was acceptable as long as memory and storage were modular, because guessing what class of cpu would sell more was easy.
So you can see why this is generally used for low end products, so they can produce one or two boards and thats it. A tactic used in laptops lately was to solder 4GB-8GB DDR4 and offer one extra slot. Not sure if the same can be done with LPCAMM2.
Also for things like Strix Halo we are talking about 32 and 64GB of LPDDR5X, who is going to solder all of that? it is far too risky.