About the ideas behind the two prototypes for a full featured Campaign, I think the main difference is the way you can connect each "chapter" on these 2 models: if what the player build in a chapter is preserved for next chapter, this itself can represent a connection between chapters; if you start each chapter with some generic pre-built layout, some kind of story would be more "needed" to connect the chapters.
Maybe the question can be viewed as if you want more a full tutorial for these players already convinced (bought the game) so the important thing is to teach mechanics, or a demo to attract new players so the thing is to tease features.
If there would be two or more campaigns, being one of them a tutorial (that doesn't need story, or not much) and other/s campaign/s that fulfill the love for RPG elements in a game (so a story is a good addition), a demo could be the first chapter of some story-driven campaign, or maybe the complete tutorial, or even a composition of both.
For me, the first thing to define should be if I want a lone campaign decent for all, or better for some option; so I would first define what I understand for each of these terms.
1. Freeplay: procedurally generated map with or without any built structures, presenting a generic objective.
2. Sandbox: a variant for freeplay mode that allows "cheating" to kill enemies, get items, edit the terrain, etc.
3. Scenario: hand-designed map with some already built structures, presenting some challenge as a serie of objectives.
4. Campaign: collection of scenarios, connected through some kind of story.
5. Tutorial: a mini-campaign focused into teaching the basics of the game to new players.
6. Demo: a complete or limited way to experience the game, usually through a chapter of a campaign, or a scenario...
So the tutorial does not fit (for me) as a demo; to serve as demo as well as tutorial, the campaign will meet more issues, and could be more difficult to get a good product to fulfill both roles.
EDIT:
Thinking about the possibilities for campaigns and scenarios and to help everybody to understand what I tried to say, I will add here some ideas I collected through time with no clear determination to use myself (feel free to use it).
Ideas for some scenarios and/or campaigns
Belts.
Belts.1- Fix a burner base to feed coal everywhere, as there is no water nearby so it need to run without electricity. Expand it to include new productions.
Belts.2- Create a complete mall to feed up a few new engineers that will work on neighbour bases (belts, inserters, assemblers, power poles, etc), constrained to the current science: just belts (without bots).
Belts.3- Fix failures on a main bus system (fix bottlenecks, balance where needed, increase production of certain item...). Expand it to include another item type then expand the base to use that item in another section (yellow/purple science, for example).
Combat.
Combat.1- Fight your way to certain area (some existing old buildings, or some ore patches...), then complete some objective (amount of production, or research certain technology...).
Combat.2- Improve your defenses (increase ammo production or delivery, expand perimeter defense...) to survive certain amount of attacking waves.
Combat.3- Recover an existing subterranean base by clearing enemies inside (they invaded our facilities).
Trains.
Trains.1- Connect by trains a few existing blocks/bases, and add enough trains to reach certain rate of deliveries (plates from smelters on base A to assemblers on base B, electronic circuits from base B to assemblers on base C, ...). Create some new blocks (to make some science packs, to use it on labs...) and repeat expanding blocks until you reach certain science production.
Trains.2- Modify an existing rail network to improve throughput. Add or change signals, make some waypoints to reroute some trains alleviating the traffic on certain bottleneck, redesign the system to use a better (faster) fuel...
Bots.
Bots.1- Fix the current bots system to avoid failures: lots of bots waiting to charge batteries on same spot, too long time to deliver certain stuff from point A to point B...
Bots.2- Create a complete mall to feed up a few new engineers that will work on neighbour bases (belts, inserters, assemblers, power poles, etc), including a section for combat (armors, equipment, combat bots...). Use bots to periodically load a train with supplies to send to these bases.
Circuitry.
Circuitry.1- Add circuitry (combinators and wires) as needed to restrain the power consumption of a block on an existing base below certain treshold, while maintaining the production rate of certain item type above certain threshold. Expand the idea to more blocks on the same base, with higher difficulty each time.
Circuitry.2- Design some circuitry to control the loading of trains to supply materials from a base/block to another base/block (neighbour engineer?) per request. The requests will be more complex over time, and will reach you through signals on red wire over power poles. Expand the system by requesting raw materials through signals on green wire.
Layout.
Layout.1- Expand an existing subterranean base to increase the production rate to certain value. The classic repeatable blueprints will not fit, as there are certain extremely hard rocks that you cannot excavate with the current technology. Expand the base to produce more item types. The layout could be carefully hand designed for a campaign, or procedurally generated for a scenario.
Layout.2- Work your way from a point (classic start with almost nothing, or advanced start with some basic already built base) to the rocket launch, by building your stuff on several restricted areas. For example, several areas shaped like capital letters (A, B, C, D...) with approx. the same amount of usable tiles each. What for is best the area shaped "M"?
Economy.
Economy.1- Play a game with certain resource type limited to certain amount. The limitation could be chosen, or set to random (among the possible options). It is very different if you limit iron ore, provided electric power, no smeltery and limited amount of plates, limited total amount of inserters or assemblers...
Economy.2- Play a market game, where certain resource type is available just by market, paid by coins you get by providing the market with a variable demand of different stuff. Electricity could be a good stuff to limite through market, but it could work also for any resource. If you need to sell or buy some fluid, you need to barrel/unbarrel.