Proper strings and arrays for starters, instead of being pointers that the programmer is responsible for doing length housekeeping.

I think what C is missing is everything that people fall back onto clever use of pointers and macros to implement. Not that I think C should have all those things, Zig does a decent job of showing alternatives.

That task would be beyond my skills, as I said, I am just a hobbyist. I think it would be interesting to see what would result from going back to one of those early foundational languages and developing a modern language from it. With a language like Algol we don't have the decades of evolution (baggage) which are a big part of languages like C and C++ and trickle into the languages they inspired even if they are trying to remove that baggage. So, what would we get if we went back to the start and built a modern language off of Algol? What would that look like?