I agree that a gamified account funding system, something along these lines is definitely the most robust and generic solution that has been proposed. I personally think that the Steem Keychain project by @aggroed and @yabapmatt looks very promising in terms of keeping keys private while still allowing easy access to sites in the Steem eco-system.
The resource credits available to dApp operators - even those with decent delegations, is not high enough to produce enough accounts to respond to a really successful onboarding drive and marketing campaign - plus the accounts still need some kind of Steem Power to be functional after they have been created anyway. Therefore, some means of allowing new users to fund their own account is great and something like the described approach could definitely work well.
The code to manage this process can be open source and generic enough to work on any dApp, so really the work for this could be achieved as a community project among the coding teams of all dApps that want to participate. While this might draw together a decent amount of human power to get the work done, it also means teamwork between groups who so far haven't worked together so much (afaik) - so this could also be an important bridge in that way too.
@steempassport was created with the aim of solving all problems relating to onboarding, but since @Steemonboarding is focused into the education and marketing, for now we will focus more on the technical side - which means looking at the challenge of this kind of account creation process. We have some other options to fund new accounts too, but that is a less technical option and one that needs more planning and organisation before it can be worked on and rolled out. We are working on that in the background too though and we have some promising plans.
I will share this post of yours into the steempassport Discord server and also look to start making some kind of high level schematic for how this system might work. :)
Also, one point that I don't think was mentioned much.. Each dApp can have a way of listing the users that are in the 'trial' process so that the community can check them out and help onboard them with upvotes if they want. This helps outsource the job of filtering spammers out to the community, which is perhaps the most efficient way to do it. Ultimately there could even be some kind of onboarding bonus for users who 'curate' the best new users towards their full account.. But one step at a time ;)