Be you rest assured, the models with soldered RAM will continue to have soldered RAM.
This is so Dell can have the cost savings of configurable RAM, combined with revenue boost of forcing customers into an overpriced upgrade at time of purchase.
Dell almost certainly will not sell these modules to end users, but if they do they will be many times more expensive than the industry standard.
I'm really getting sick of all the extreme anti-customer monetization that tech companies are allowed to get away with. Duopolies/oligopolies aren't any better than Monopolies, and price-fixing/anti-trust laws are never enforced.