The way I've seen the expansion of the universe described, it seems to work a bit like an inside-out black hole: an event horizon beyond which there is no causal connection, light from beyond it can't reach us. The Big Rip is that event horizon getting ever closer (to all points at once rather than just "us", so the analogy is imperfect).
Answers to other questions here say that the equivalent of Hawking radiation in this context is Unruh radiation. If I understand correctly, Unruh radiation gets hotter as acceleration increases, which in this case also makes it like Hawking radiation, by increasing as the surface area of the event horizon shrinks.
I understand that there is some argument about whether or not Unruh radiation creates observable particles in the same way that Hawking radiation does.
If Unruh radiation does in fact create particles, would the positive gravitational pressure from these particles be expected to balance the negative pressure (whatever causes it) that is causing the accelerating expansion of the universe?
If the balance was perfect, I think this would prevent the acceleration from increasing, would my reasoning imply that current evidence says Unruh radiation doesn't create observable particles in the same way that Hawking radiation does?
(My physics level: enthusiastic amateur, I've tested myself with past exam papers as at least a good AS-level in the UK, and have formal qualifications of maths and further maths at A2 level, but my degree is software, not physics).