Now they force you to pay 2.3k GBP to publish an article. Previously it was free, unless you wanted it to make it immediately accessible on the website. People in astrophysics always did put articles on arxiv.org anyway, so papers were already accessible to everyone (in a non-typeset/not-proofread form), but now it will be the same, but everyone will have to pay 2.3 kGBP per paper. Also a useful comparison. The subscription to MNRAS for the institution was 6.5 kGBP. So any institution that publishes more than 2 papers a year will pay way more then before. Also none of the referees are payed. Also, some funding agencies (like UK's UKRI) prohibit to put page charges in overheads for grants, so I wonder how people are supposed to get the money...
To be honest, the natural consequence of this will be that people will stop publishing in MNRAS. There is simply not enough value added in the publication process to justify 2.3k GBP, given that the referees are not payed, the journal is published online only, and the arxiv already provide hosting.
Also, this is the case of Royal Astronomical Society (which does a lot of good things: provides grants, fellowships, organizes meetings, gives prizes) of trying to preserve the income stream to fund that. This is wrong, and we should not accept that in my opinion.