For example, building more farms than your system needs to feed the people (which is not even a metric right now, unfortunately)
I'll wait until we know more about what the "Standard of Living" score does before commenting on whether it's a metric or not.
Maybe bump the distance limit for claiming to appease the people who want to expand to some specific far-off point, to balance out that there will be fewer (abandoned) systems being created.
From Frontier's official stats there must be at the very least 13,000 distinct system architects, and there could easily be almost double that.
Slowing down the rate at which people can claim
second systems would barely have touched the initial rush (I certainly don't intend to claim a second one, given how much space this first one still has left). Yes, there are a few prominent chains - though mostly made by groups, who again wouldn't be slowed at all by a "one per architect" limitation - but most of the reason there's a lot systems is there's a lot of different people.
Will they though? Noting that, from Inara stats, Powerplay 2.0 has slowly grown to about 40% participation with no massive spike followed by a reduction.
Though - more as expected - the total number of merits over time (and the resulting rate of change of system ownership and strength) does seem to have gradually decreased. It's held up well but it's certainly not as
engaged with a feature as it was on release, as is only to be expected.
Of course, if colonisation were to level off and stabilise at even 20% of its initial rate that would still be many thousands of new systems a month.