Exercise 3: Why Checkpoints and LoRAs Have No Equivalent on Midjourney or DALL-E — Possible Solution
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WHAT CHECKPOINTS AND LORAS ACTUALLY REQUIRE
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Per this chapter, "because Stable Diffusion's weights are public, the
community has trained thousands of alternate checkpoints -- full,
re-trained or fine-tuned versions of the base model." A checkpoint is
only possible to create and distribute because the base model's own
weights are openly available for someone outside the company that
built it to load, fine-tune, and redistribute. LoRAs, per this chapter,
are "smaller, lighter-weight adapter files that can be layered on top
of a checkpoint" -- but that layering itself only works because the
base checkpoint being layered onto is something a third party can
actually load and run in the first place.

WHY THIS DEPENDS DIRECTLY ON OPENNESS
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Both mechanisms presuppose direct access to the underlying model
weights: to create a new checkpoint, someone needs the base model file
itself to fine-tune; to apply a LoRA, someone needs to load both the
LoRA file and a compatible base checkpoint into their own generation
pipeline. Neither operation is possible against a model that only
exists behind someone else's API or hosted service, with no
downloadable weights at all.

WHY imgai1-4's WARN-BOX EXPLAINS WHY MIDJOURNEY CAN'T OFFER THIS
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Per imgai1-4's own warn-box, "Midjourney doesn't publish its model
architecture or training details" -- there are no weights available
to fine-tune into a new checkpoint, and no base model file a user
could load a LoRA against, because the model only runs on Midjourney's
own servers and is never distributed to users at all. The same
reasoning applies to DALL-E (imgai1-6), which is likewise a closed,
hosted-only model with no distributed weights. In both cases, the
structural requirement checkpoints and LoRAs depend on -- a
downloadable, loadable base model -- simply doesn't exist.

WHY THIS IS A STRUCTURAL DIFFERENCE, NOT A MISSING FEATURE
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This isn't a case of Midjourney or DALL-E choosing not to build a
checkpoint/LoRA feature -- it's that the entire mechanism depends on a
precondition (open, distributable model weights) that closed, hosted-
only tools don't meet by design. This is exactly the same open-vs-
closed distinction imgai1-4's own warn-box drew for describing
behavior vs. mechanism, applied here to a genuinely different
consequence of that same underlying difference.

WHY THIS WORKS AS AN ANSWER
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It explains what checkpoints and LoRAs structurally require (loadable,
distributable model weights), and connects that requirement directly
back to imgai1-4's own warn-box about Midjourney's closed architecture
to explain why neither Midjourney nor DALL-E can offer an equivalent
capability, as a structural consequence rather than a missing feature.