In my effort to make the Bitcoin codebase more mature, and most of all multi-threading, I got limited a for a long time by the UTXO. A central component that has issues with multi-threading and is a bottleneck for bigger blocks.
I finished a prototype implementation for a new UTXO database in the Flowee project which may be interesting to many in order to allow scale to real gigabyte blocks.
Please see my report I posted on yours; https://www.yours.org/content/19ff35ba5c94