I don't think you need fast read access to the utxo set after IBD, because you have an average of 10 minutes to validate new blocks and that's enough time to do it with slow read access

*during* IBD, I think it's a different story. But even there, MergeSync looks promising. It lets users download the blockchain first, without validating changes to the utxo set, and then *afterwards* efficiently extract the utxo set by creating an array representing all tx inputs ever used in any transaction in any block (in the format txid:vout) and injecting into that same array all tx outputs ever created (in the same format), and then removing all duplicates. What you're left with is the utxo set, without needing to update it *during* IBD.

combining these two ideas, I think you can run a fully validating node without fast read access to the utxo set, i.e. with low ram requirements. Just use MergeSync to do IBD, and after that, slow read access suffices