Thanks all. Unsurprising results, but it's always good to check assumptions.
(Though I did think we had a few more lurkers who might vote.)
The chronological timeline and broken algorithm appears to be a really common frustration.
It's also easy to solve, even for a feed with lots of items, (so long as you're not completely "WOOOOO!!!!!! SUPER SMART ALGOS!!! MACHIEN LERNIN GUD!!!!¬``" I guess).
On the user base issue, I see critical mass as a problem as much as a goal.
Yes, if there's a need of connections it's a catch 22, but if the service can be sufficiently useful before you have those connections it can be a multi-stage process.
The issue then is knowing if/when critical mass is going to hit - because it means costs sky rocketing, which needs balancing by an equivalent income or existing funds to avoid an expensive failure. If enough people were willing to pay for escaping FB then it would simplify matters - I didn't expect that, but it would be the easiest option so worth verifying.