Full disclosure: I have no affiliation with the author, but I'm sharing because I genuinely believe in the work.
There's a practically unending list of undefined/implementation defined behaviours, which is great if you want to implement an ultra minimal microcontroller with 100 flops, but pretty awful otherwise.
Requiring the C (compressed) extension in the RVA profiles was definitely a mistake. The lack of true 16/64kB pages and conditional moves are probably a mistake (though fixable).
I don't know how any of these make it more robust and mature.
(But to be clear, I still think it's pretty good overall.)
Requiring C (compressed) is necessary to avoid splitting the Linux ecosystem. Chips lacking C would never be able to run binaries compiled with C. There's no practical way for such binaries to detect this and work around it at runtime as they can with other extensions. And emulation would be super-slow given a large proportion of instructions are compressed.
Also the excuse given by Qualcomm - that it would make all instructions fixed length and so much easier to decode - is just wrong. RISC-V supports variable length instructions, even much longer than 32 bits, and you've just got to deal with it. Just because Qualcomm acquired a company with a microarchitecture that could only deal with fixed length instructions is no reason to break the ecosystem.
Also interested in the problems you see in Zicond. It claims at least to give you most of the benefit of conditional moves using only two instructions, but I've not actually tried using it. (https://docs.riscv.org/reference/isa/extensions/zicond/_atta...)
RISC-V Microprocessor System-On-Chip Design is written to be accessible to an advanced undergraduate audience with limited background. It explains concepts from operating systems, VLSI, and memory systems as necessary, and High school mathematics is sufficient preparation for most of the book, although the floating point and division chapters will be primarily of interest to those with a curiosity about computer arithmetic. Like Harris and Harris’s Digital Design and Computer Architecture textbooks, this book will appeal to students with easy-to-read and complete explanations, sidebars, and occasional humor and cartoons.
It comes with an open-source implementation and will include end-of-chapter problems to extend the RISC-V processor in various ways. Ancillary materials include a GitHub repository with complete open-source SystemVerilog code, validation code in C and assembly language, and code for benchmarking and booting Linux.