I understand the creation request goes to a instance with the most RC available, but shouldn't @hiveonboard be such instance as well?

Yes you are right, it haven't made it in the architecture picture but the code available actually is using @hiveonbard as a backup account creator as well.

A built in referral system would be a cancer and a paradise for spammers. Please don't suggest that.

There is an idea around, where there is ZERO incentive for spammers using this. Details on this will follow, there won't be a feature which will encourage spam - I totally agree on that.