Not sure I agree with that reasoning. Sure, if the egress cost is something they cannot lower that would be the case, but since they initially charged nothing thats unlikely. The argument for the new egress tax (torrenting and stuff) wouldnt need to apply to db backups.
With 30 bucks a month for backups, that I would also need to set up myself via s3, it would be a much worse deal than something managed like neon or planetscale. So I fear it would effectively make Railway db hosting non competitive for going into production.
Conversely, a simple to use native backup solution with competitive costs would make Railway a viable option for more (and more serious aka willing-to-pay) users