Not necessarily for your vision but for your goal of generating recurring and non-linear income, the question may be 'What is fairly quick/simple to code that will generate ongoing income for very little management, maintenance and promotion?'
Out of the options listed there Market Maker seems the most lucrative & least time consuming for you personally to get out the way because it can be outsourced.
Uphold/BitReserve, NuShares/Tether & numerous others are all building their businesses around BitAssets, unlike Bitcoin there is no large established market leader, yet...
All these businesses are doing nothing else besides trying to establish, often at times a single BitUSD.
BTS is in a great position here, it has already developed the best blockchain and a good BitUSD and has access to dilution to incentivise liquidity providers.
It also doesn't require large amounts of capital, only enough dilution to provide an incentivising yield for others to provide capital. It seems liquidity operations on external exchanges can be outsourced to NuShares liquidity pools or others like Alt.
It seems like very little work and a worker contract paying a few thousand dollars a month could bootstrap BitUSD/Gold liquidity on external exchanges to see if increased liquidity increases BTS value and Smartcoin adoption.
I'm sure it can be done independently but once that most likely to complete BitAssets action & increase BTS value is out the way it requires very little more of your time.
Gambling might not be do-able for the reasons you mentioned but if a third party added a game of chance FBA to BTS that would be an immediate earner that would bring in income everyday for very little upkeep.
Starting a new business like MAS, as you've experienced with BTS, is a hard process that always takes longer and costs more than you think and has a high probability of not finding a market easily. It also requires expertise & or collaboration in other areas like management and promotion which are time consuming & perhaps not your strong suits.
Stealth also fits the profile as there's money on the table and perhaps opportunity to earn recurring income.
The BitUSD savings club may be relatively simple to code, but requires very little maintenance/management. So if 0.X% went to the creator and new club started every month and could be applied to multiple BitAssets then that would provide a constant income stream from day 1.
https://bitsharestalk.org/index.php/topic,20648.msg266463.html#msg266463