KissMyRearHayley That's a shame, it just seems like something super easy to do.
Getting it done might indeed not be that hard. One way to measure how hard it would be would be to do it and record how long it took (see advice from GlitchDefense).
After it's done there is still some work to test it. Right now GrapheneOS builds for 15 devices, and some of them (Fold and Tablet) have screens that are genuinely different.
After it's done and tested it needs to be maintained. That might include, for each release, for 15 devices, making sure that both the monospaced font and the proportional font work, because there is always the possibility that Google would ship new font-rendering code that would do something wrong (or even, perhaps, crash) on the new font.
It would genuinely not be impossible to do! Doubtless other Android variants do it! But so far 100% of those other Android variants are behind GrapheneOS on security updates. So far the GrapheneOS team has chosen to focus on things like sandboxing Google Play, hardening the user-space and kernel storage allocators, improving control-flow integrity, MTE support, fixing firewall leaks, adding the duress-PIN feature, etc.