The reason this rule was introduced on old OGS (which was correspondence only, so no possibility to play live games in between correspondence timeouts), back around 2010 I guess, was there was a player luke a 5d who left the site and mass timed out down to 5k or whatever, who then returned and re-entered tournaments which seeded based on rating with his 5k rating and upset people who got crushed.
So one obvious alternate solution to this problem rather than an automatic serial correspondence timeout rule would be to let the timeouts happen and be rated, and then when he returns reset his rank to 5d. The downside is this does introduce extra rating points into the rating system so is inflationary, but if it is manual and rare might be ok. Rating systems do generally need points injected over time anyway to cope with people getting stronger (the delta value in the EGF rating system, does OGS glicko2 have similar?).
Another would be not trying to let that human use the same account, so instead he needs to make a new account (which will have lower volatilty) and play some ranked games to get back to a realistic 5d rank before being allowed to enter a tournament which seeds based on ranks. This is extra work for tournament directors though to screen out the inaccurate ranked people. Also it’s not only relevant to tournaments (though is more annoying when a 5d as a 5k wins some kyu division) but also affects the regular ranked games played by a 5k vs this 5d as a 5k who wants to play a real 5k.