I went through the trouble of creating an account to say this, apologies if it's already been said somewhere in the previous 43 pages.
I stumbled about the Unknown Realm kickstarter page by chance earlier this evening, followed by this thread when I went looking for a review, or status of the project. I was curious because...
...from what I can see displayed on the kickstarter, I'm pretty confident that what is presented cannot be created on a non-expanded/stock (memory wise, at the least) C64, unless that cartridge has a additional RAM built in, or they go with a large number of floppies and a crazy amount of swapping (assuming this is to run a real C64, and not an emulator that can get around these limitations, at least somewhat).
I'm 50 now. I got my C64 when I was 12-13 and spent so much over the next 5+ years on it (learning how to program, mainly) that my spine was growing in crooked from all the sitting, and had to have some medical assistance. I still remember, and have a good feel, for what is and is not possible given the limitations (ie- even if you use some of the 'clever' raster tricks for graphics in ASM, or the hidden 'ram-under-rom' area that boosts things to around 80k, etc).
I just felt compelled to share my take, as I owe the C64 a very large thanks for where my life ended up going (for the better).
I'm about in the same boat!
If you're interested in a quick rundown about the cartridge: https://rentry.co/unknownrealm#game-cartridge
A guy creating flash cartridges tried to talk to Bruce early in development, but he refused any help since he had the cartridge done by 2017:
https://twitter.com/pagan_realm/status/1672941094131179522/photo/1