Doing so would alter the bill to clearly favor registration requirements over activity requirements, which I do not believe is a good solution. Using activity requirements for voting can prevent bloating of the game with obscene amounts of recruits without scaring away new members of the forum who wish to participate. Any off-site recruit or whatever that does not meet the activity requirements would be simply rendered irrelevant. Those who show an active interest would be able to vote.
What this of course ignores is that Atlasia is, fundamentally, a game for Atlas users. It was initially built as the mock government for the Atlas community and to this day is intrinsically linked with the forum's at-large userbase. Under your proposal, however, this notion is eradicated. A longtime Atlas user who has a slightly quiet month or two will suddenly find themselves ineligible, while (as we've seen), someone can ask a number of non-Atlas users to make an account and quickly make [n] posts as a favor to them, then register and then come back a week later to vote.
A registration requirement is the easiest way to fix this: set the requirement to be a number of posts that's too high for someone to make just "as a favor" to someone else to vote for them in the game; rather, it's a number of posts that demonstrates an at least somewhat active interest in the forum, its discussion, and its community. We've seen that people are willing to make 15 posts as a favor; however I highly doubt the uninterested would be even remotely willing to make
50.
Setting the similarly scaled requirements as activity requirements - say 50 posts in 8 weeks - then this is prohibitive on even a number of regular Atlas users. If you look at this most recent election under this rule? Windjammer, who was elected president at it, would be invalid. Muaddib, an incumbent house rep, invalid. Fhtagn, invalid. So on and so forth.
Thus using solely a recent activity requirement cannot, alone, ensure that the participants in this game are all genuinely committed users of the forum without making the requirement objectively ridiculous - a robust initial registration requirement is a necessity as well.