OTOH it is also optimistic on the nitrogen sequestering, simply uses a Redfield ratio on the above organic storage, and an optimistic one to boot. (6 compared to 10 on the paper I found. That is also comparable to the ratio of carbon:nitrogen fixation in soils (at PNK usage), so ~ 10 seems like a fair number.) But yes, according to these figures Earth has already stored away ~ 1 bar of nitrogen. Remains to find the evidence.

It isn't difficult to see why it is a tenuous model.

OTOH it seems to be testable, at least the authors think so. And there are AFAIU indications on sequestering and release of gases in atmospheres, such as claims that Earth dense atmosphere initially were at 10 bars of mostly CO2, the probable out-gassing of enough hydrogen to make Earth go from a reducing to an oxidizing atmosphere, and the later release of 20 % oxygen. Obviously then atmospheric, geological and biological processes have transformed the atmosphere completely.

So I am very curious and would be grateful for any examples from planetary history showing that nitrogen sequestering isn't feasible.

As for the raising of the Earth's orbit, this was proposed by Korycabsky, Laughlin and Adams back in 2001. The mechanism they propose is similar to what I found with Jupiter's nudging of the Earth. The authors above suggested a 5000 period of nudging the Earth by pushing a comet to the inner solar system. Jupiter lacks the highly elliptical orbit, but it has a lot more mass.